elf-built flmsg 4.0.8 from source and same result. 

Self-built fldigi 4.1.03 and self-built flmsg 4.0.8 *do* run together.

Looks like I built flmsg 4.0.8 for rawhide at the time (f30) but forgot to do the other builds. They've been submitted.

flmsg-4.0.8-1.fc28 has been submitted as an update to Fedora 28. https://bodhi.fedoraproject.org/updates/FEDORA-2019-0f04f0cf96

flmsg-4.0.8-1.fc29 has been submitted as an update to Fedora 29. https://bodhi.fedoraproject.org/updates/FEDORA-2019-e2fdae25b3

FWIW just upgraded to 30 and the same crash. I have:
 
fldigi.x86_64                      4.1.03-1.fc30                      @updates
flmsg.x86_64                       4.0.8-1.fc30                       @fedora

flmsg-4.0.8-1.fc28 has been pushed to the Fedora 28 testing repository. If problems still persist, please make note of it in this bug report.
See https://fedoraproject.org/wiki/QA:Updates_Testing for
instructions on how to install test updates.
You can provide feedback for this update here: https://bodhi.fedoraproject.org/updates/FEDORA-2019-0f04f0cf96

flmsg-4.0.8-1.fc29 has been pushed to the Fedora 29 testing repository. If problems still persist, please make note of it in this bug report.
See https://fedoraproject.org/wiki/QA:Updates_Testing for
instructions on how to install test updates.
You can provide feedback for this update here: https://bodhi.fedoraproject.org/updates/FEDORA-2019-e2fdae25b3

This message is a reminder that Fedora 28 is nearing its end of life.
On 2019-May-28 Fedora will stop maintaining and issuing updates for
Fedora 28. It is Fedora's policy to close all bug reports from releases
that are no longer maintained. At that time this bug will be closed as
EOL if it remains open with a Fedora 'version' of '28'.

Package Maintainer: If you wish for this bug to remain open because you
plan to fix it in a currently maintained version, simply change the 'version' 
to a later Fedora version.

Thank you for reporting this issue and we are sorry that we were not 
able to fix it before Fedora 28 is end of life. If you would still like 
to see this bug fixed and are able to reproduce it against a later version 
of Fedora, you are encouraged  change the 'version' to a later Fedora 
version prior this bug is closed as described in the policy above.

Although we aim to fix as many bugs as possible during every release's 
lifetime, sometimes those efforts are overtaken by events. Often a 
more recent Fedora release includes newer upstream software that fixes 
bugs or makes them obsolete.

I did a simple rebuild for f30 here:

https://koji.fedoraproject.org/koji/taskinfo?taskID=34600116

Please try it and see if it solves the problem before I report it upstream.

Assuming x86_64 this should work:

dnf reinstall https://kojipkgs.fedoraproject.org//work/tasks/169/34600169/flmsg-4.0.8-1.fc30.x86_64.rpm

flmsg-4.0.8-1.fc28 has been pushed to the Fedora 28 stable repository. If problems still persist, please make note of it in this bug report.

flmsg-4.0.8-1.fc29 has been pushed to the Fedora 29 stable repository. If problems still persist, please make note of it in this bug report.

Still seeing this behavior in FC28 with
 
fldigi.x86_64                      4.1.03-1.fc28                      
flmsg.x86_64                       4.0.8-1.fc28 
flxmlrpc.x86_64                     0.1.4-8.fc28           

and on FC30 with 

fldigi.x86_64                       4.1.03-1.fc30                      
flmsg.x86_64                        4.0.8-1.fc30                        
flxmlrpc.x86_64                     0.1.4-10.fc30                      

Same exception: 

/usr/include/c++/9/bits/stl_vector.h:1042: std::vector<_Tp, _Alloc>::reference std::vector<_Tp, _Alloc>::operator[](std::vector<_Tp, _Alloc>::size_type) [with _Tp = unsigned char; _Alloc = std::allocator<unsigned char>; std::vector<_Tp, _Alloc>::reference = unsigned char&; std::vector<_Tp, _Alloc>::size_type = long unsigned int]: Assertion '__builtin_expect(__n < this->size(), true)' failed.

Caught signal 6
Aborting fldigi due to a fatal error.
Please report this to:   fldigi-devel
or file a bug report at: https://fedorahosted.org/fldigi/newticket

****** Stack trace:
fldigi(+0x370258)[0x555703a7f258]
fldigi(+0x370516)[0x555703a7f516]
/lib64/libpthread.so.0(+0x12e70)[0x7fa6c9528e70]
/lib64/libc.so.6(gsignal+0x145)[0x7fa6c87c7eb5]
/lib64/libc.so.6(abort+0x127)[0x7fa6c87b2895]
fldigi(+0x102a88)[0x555703811a88]
fldigi(+0x11a6ef)[0x5557038296ef]
fldigi(+0x13294c)[0x55570384194c]
fldigi(+0x13473b)[0x55570384373b]
fldigi(+0x131653)[0x555703840653]
fldigi(+0x13191c)[0x55570384091c]
fldigi(+0x131e40)[0x555703840e40]
fldigi(+0x13102f)[0x55570384002f]
fldigi(+0x13128c)[0x55570384028c]
fldigi(+0xf5f43)[0x555703804f43]
/lib64/libpthread.so.0(+0x85a2)[0x7fa6c951e5a2]
/lib64/libc.so.6(clone+0x43)[0x7fa6c888b163]

****** Version information:
fldigi 4.1.03
Copyright (C) 2007-2010 Dave Freese, Stelios Bounanos, and others.
License GPLv3+: GNU GPL version 3 or later <http://www.gnu.org/licenses/gpl-3.0.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

****** Build information:
Build information:
  built          : Mon Apr 22 13:57:16 UTC 2019 by mockbuild@ on x86_64-redhat-linux-gnu for x86_64-redhat-linux-gnu

Ok, was hoping a simple rebuild would fix it. Ill follow up with Dave.

Ok, Dave sent me some test versions I have have them building on my COPR:

https://copr.fedorainfracloud.org/coprs/hobbes1069/NBEMS/

Please test these builds by downloading the package (or enabling the COPR in dnf) and report back if they fix the problem.

Sorry for the delay getting back. I have to report that the COPR build of fldigi also crashes when flmsg is started:

/usr/include/c++/9/bits/stl_vector.h:1042: std::vector<_Tp, _Alloc>::reference std::vector<_Tp, _Alloc>::operator[](std::vector<_Tp, _Alloc>::size_type) [with _Tp = unsigned char; _Alloc = std::allocator<unsigned char>; std::vector<_Tp, _Alloc>::reference = unsigned char&; std::vector<_Tp, _Alloc>::size_type = long unsigned int]: Assertion '__builtin_expect(__n < this->size(), true)' failed.

Caught signal 6
Aborting fldigi due to a fatal error.
Please report this to:   fldigi-devel
or file a bug report at: https://fedorahosted.org/fldigi/newticket

****** Stack trace:
fldigi(+0x370648)[0x5627e1902648]
fldigi(+0x370906)[0x5627e1902906]
/lib64/libpthread.so.0(+0x12e70)[0x7f8858ee8e70]
/lib64/libc.so.6(gsignal+0x145)[0x7f8858187eb5]
/lib64/libc.so.6(abort+0x127)[0x7f8858172895]
fldigi(+0x102dd8)[0x5627e1694dd8]
fldigi(+0x11ab1f)[0x5627e16acb1f]
fldigi(+0x132d8c)[0x5627e16c4d8c]
fldigi(+0x134b6b)[0x5627e16c6b6b]
fldigi(+0x131a93)[0x5627e16c3a93]
fldigi(+0x131d5c)[0x5627e16c3d5c]
fldigi(+0x132280)[0x5627e16c4280]
fldigi(+0x13147f)[0x5627e16c347f]
fldigi(+0x1316dc)[0x5627e16c36dc]
fldigi(+0xf62b3)[0x5627e16882b3]
/lib64/libpthread.so.0(+0x85a2)[0x7f8858ede5a2]
/lib64/libc.so.6(clone+0x43)[0x7f885824b163]

****** Version information:
fldigi 4.1.04.08
Copyright (C) 2007-2010 Dave Freese, Stelios Bounanos, and others.
License GPLv3+: GNU GPL version 3 or later <http://www.gnu.org/licenses/gpl-3.0.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

****** Build information:
Build information:
  built          : Sat May 11 13:17:02 UTC 2019 by mockbuild@ on x86_64-redhat-linux-gnu for x86_64-redhat-linux-gnu

  configure flags: '--build=x86_64-redhat-linux-gnu' '--host=x86_64-redhat-linux-gnu' '--program-prefix=' '--disable-dependency-tracking' '--prefix=/usr' '--exec-prefix=/usr' '--bindir=/usr/bin' '--sbindir=/usr/sbin' '--sysconfdir=/etc' '--datadir=/usr/share' '--includedir=/usr/include' '--libdir=/usr/lib64' '--libexecdir=/usr/libexec' '--localstatedir=/var' '--sharedstatedir=/var/lib' '--mandir=/usr/share/man' '--infodir=/usr/share/info' 'build_alias=x86_64-redhat-linux-gnu' 'host_alias=x86_64-redhat-linux-gnu' 'CXXFLAGS=-O2 -g -pipe -Wall -Werror=format-security -Wp,-D_FORTIFY_SOURCE=2 -Wp,-D_GLIBCXX_ASSERTIONS -fexceptions -fstack-protector-strong -grecord-gcc-switches -specs=/usr/lib/rpm/redhat/redhat-hardened-cc1 -specs=/usr/lib/rpm/redhat/redhat-annobin-cc1 -m64 -mtune=generic -fasynchronous-unwind-tables -fstack-clash-protection -fcf-protection' 'LDFLAGS=-Wl,-z,relro -Wl,--as-needed -Wl,-z,now -specs=/usr/lib/rpm/redhat/redhat-hardened-ld' 'CFLAGS=-O2 -g -pipe -Wall -Werror=format-security -Wp,-D_FORTIFY_SOURCE=2 -Wp,-D_GLIBCXX_ASSERTIONS -fexceptions -fstack-protector-strong -grecord-gcc-switches -specs=/usr/lib/rpm/redhat/redhat-hardened-cc1 -specs=/usr/lib/rpm/redhat/redhat-annobin-cc1 -m64 -mtune=generic -fasynchronous-unwind-tables -fstack-clash-protection -fcf-protection' 'PKG_CONFIG_PATH=:/usr/lib64/pkgconfig:/usr/share/pkgconfig'

  compiler       : gcc version 9.1.1 20190503 (Red Hat 9.1.1-1) (GCC) 

  compiler flags : -I$(srcdir) -I$(srcdir)/include -I$(srcdir)/irrxml -I$(srcdir)/libtiniconv -I$(srcdir)/fileselector -I$(srcdir)/xmlrpcpp -I$(srcdir)/mbedtls -pthread -I/usr/include/alsa -D_REENTRANT -pthread -I/usr/include/libusb-1.0 -I/usr/include/libpng16 -pipe -Wall -fexceptions -O2 --param=max-vartrack-size=0 -I$(srcdir)/xmlrpcpp --param=max-vartrack-size=0 -DNDEBUG

  linker flags   : -lportaudio -lm -lpthread -lasound -lfltk_images -lfltk -lX11 -lsndfile -lsamplerate -lpulse-simple -lpulse -lhamlib -lpng16 -lz -ldl -lpthread

  libraries      : FLTK 1.3.5
                   libsamplerate 0.1.9
                   libsndfile 1.0.28
                   PortAudio 19
                   PulseAudio 12.2-rebootstrapped
                   Hamlib 3.3

Runtime information:
  system         : Linux elvostro 5.0.16-300.fc30.x86_64 #1 SMP Tue May 14 19:33:09 UTC 2019 x86_64

  libraries      : libsamplerate-0.1.9 (c) 2002-2008 Erik de Castro Lopo
                   libsndfile-1.0.28
                   PortAudio V19-devel (built Feb  2 2019 11:31:07) 1899
                   Pulseaudio 12.2.0
                   Hamlib 3.3

Yum installations:

Installing:
 fldigi                x86_64           4.1.04.08-1.fc30            hobbes1069-NBEMS           
Installing dependencies:
 tqsllib               x86_64           1:2.4.7-1.fc30              updates                    
 wxBase3               x86_64           3.0.4-8.fc30                fedora                     
 wxGTK3                x86_64           3.0.4-8.fc30                fedora                     
 wxGTK3-i18n           noarch           3.0.4-8.fc30                fedora                     
Installing weak dependencies:
 trustedqsl            x86_64           2.4.7-1.fc30                updates                    

Installing:
 flmsg               x86_64            4.0.9.03-1.fc30             hobbes1069-NBEMS            
Installing dependencies:
 flxmlrpc            x86_64            0.1.4-10.fc30               fedora

From a core file created by attaching gdb to fldigi: 

(gdb) where
#0  0x00007ffff71feeb5 in raise () from /lib64/libc.so.6
#1  0x00007ffff71e9895 in abort () from /lib64/libc.so.6
#2  0x0000555555656dd8 in std::__replacement_assert (__file=<optimized out>, __line=<optimized out>, 
    __function=<optimized out>, __condition=<optimized out>)
    at /usr/include/c++/9/x86_64-redhat-linux/bits/c++config.h:2533
#3  0x000055555566eb1f in non-virtual thunk to Method<RX_get_data>::execute(XmlRpc::XmlRpcValue&, XmlRpc::XmlRpcValue&) () at ./xmlrpcpp/XmlRpcValue.h:123
#4  0x0000555555686d8c in XmlRpc::XmlRpcServer::executeMethod (this=0x5555674ffba0, methodName=..., 
    params=..., result=...) at xmlrpcpp/XmlRpcServer.cpp:406
#5  0x0000555555688b6b in XmlRpc::XmlRpcServer::executeRequest (this=0x5555674ffba0, request=...)
    at xmlrpcpp/XmlRpcServer.cpp:349
#6  0x0000555555685a93 in XmlRpc::XmlRpcServerConnection::executeRequest (this=0x7fffc40031e0)
    at xmlrpcpp/XmlRpcServerConnection.cpp:230
#7  0x0000555555685d5c in XmlRpc::XmlRpcServerConnection::writeResponse (this=0x7fffc40031e0)
    at xmlrpcpp/XmlRpcServerConnection.cpp:197
#8  0x0000555555686280 in XmlRpc::XmlRpcServerConnection::handleEvent (this=0x7fffc40031e0)
    at xmlrpcpp/XmlRpcServerConnection.cpp:69
#9  0x000055555568547f in XmlRpc::XmlRpcDispatch::waitForAndProcessEvents (this=0x5555674ffbc0, 
    timeoutSeconds=<optimized out>) at xmlrpcpp/XmlRpcDispatch.cpp:259
#10 0x00005555556856dc in XmlRpc::XmlRpcDispatch::work (this=0x5555674ffbc0, timeoutSeconds=-1, 
    timeoutSeconds@entry=6.953355807148846e-310) at xmlrpcpp/XmlRpcDispatch.cpp:113
#11 0x0000555555686739 in XmlRpc::XmlRpcServer::work (this=<optimized out>, 
    timeSeconds=6.953355807148846e-310, timeSeconds@entry=-1) at xmlrpcpp/XmlRpcServer.cpp:169
#12 0x000055555564a2b3 in XmlRpcImpl::run (this=<optimized out>) at network/xmlrpc.cxx:283
#13 XML_RPC_Server::thread_func () at network/xmlrpc.cxx:283
#14 0x00007ffff7f555a2 in start_thread () from /lib64/libpthread.so.0
#15 0x00007ffff72c2163 in clone () from /lib64/libc.so.6

I haven't forgotten about this but I don't have a solution either. I've been working with Dave and for whatever reason koji/mock builds have this problem but local builds with identical configuration (as far as we can tell) do not.

I think Dave have figured out the problem, please test the following build and report back whether it's fixed.

https://koji.fedoraproject.org/koji/taskinfo?taskID=35367990

FEDORA-2019-3c302462c2 has been submitted as an update to Fedora 30. https://bodhi.fedoraproject.org/updates/FEDORA-2019-3c302462c2

fldigi-4.1.03-2.fc30 has been pushed to the Fedora 30 testing repository. If problems still persist, please make note of it in this bug report.
See https://fedoraproject.org/wiki/QA:Updates_Testing for
instructions on how to install test updates.
You can provide feedback for this update here: https://bodhi.fedoraproject.org/updates/FEDORA-2019-3c302462c2

fldigi-4.1.03-2.fc29 has been pushed to the Fedora 29 testing repository. If problems still persist, please make note of it in this bug report.
See https://fedoraproject.org/wiki/QA:Updates_Testing for
instructions on how to install test updates.
You can provide feedback for this update here: https://bodhi.fedoraproject.org/updates/FEDORA-2019-61d301c36a

fldigi-4.1.03-2.fc29 has been pushed to the Fedora 29 stable repository. If problems still persist, please make note of it in this bug report.

fldigi-4.1.03-2.fc30 has been pushed to the Fedora 30 stable repository. If problems still persist, please make note of it in this bug report.

Sorry, I thought I had updated this earlier - fldigi and flmsg are working together OK in Fedora 30.