Could you add this link with the package u202 and try your application?
ln -s /usr/lib/jvm/openjfx/libglassgtk2.so /usr/lib/jvm/java-1.8.0-openjdk-1.8.0.191.b12-11.fc28.x86_64/jre/lib/amd64/

It's seems that with u202 that have a new library libglassgtk2.so. If it's the problem, the package java-1.8.0-openjdk-openjfx.x86_64 need to be updated.

(In reply to Nicolas De Amicis from comment #1)
> Could you add this link with the package u202 and try your application?
> ln -s /usr/lib/jvm/openjfx/libglassgtk2.so
> /usr/lib/jvm/java-1.8.0-openjdk-1.8.0.191.b12-11.fc28.x86_64/jre/lib/amd64/

Adding this symlink
/usr/lib/jvm/java-1.8.0-openjdk-1.8.0.191.b12-11.fc28.x86_64/jre/lib/amd64/libglassgtk2.so -> /usr/lib/jvm/openjfx/rt/lib/amd64/libglassgtk2.so
seems to work around this crash.

But ... later on, when trying to use the app, I am observing X11-related segfaults. When downgrading openjfx, I am not observing these segfaults.

The package java-1.8.0-openjdk-openjfx will be updated. For the segfaults reported, what desktop are you using? With which kind of application you are observing these segfaults?

(In reply to Nicolas De Amicis from comment #3)
> The package java-1.8.0-openjdk-openjfx will be updated. For the segfaults
> reported, what desktop are you using? With which kind of application you are
> observing these segfaults?

I am on Xfce.

The app is MediathekView (https://mediathekview.de/). I am using upstream's binary, having been locally repackaged into a rpm.

BTW: One of reasons for me to stay with fc28 is the unpleasant situation with MediathekView/openjfx on fc29 (The version of openjfx in initial fc29 was "plain broken").
Seems to me, as if you have propagated the issues or at lease some of them from fc29 to back to fc28 :(

(In reply to Ralf Corsepius from comment #4)
> (In reply to Nicolas De Amicis from comment #3)
> > The package java-1.8.0-openjdk-openjfx will be updated. For the segfaults
> > reported, what desktop are you using? With which kind of application you are
> > observing these segfaults?
> 
> I am on Xfce.
> 
> The app is MediathekView (https://mediathekview.de/). I am using upstream's
> binary, having been locally repackaged into a rpm.
> 
> BTW: One of reasons for me to stay with fc28 is the unpleasant situation
> with MediathekView/openjfx on fc29 (The version of openjfx in initial fc29
> was "plain broken").
> Seems to me, as if you have propagated the issues or at lease some of them
> from fc29 to back to fc28 :(

Please point us to the bug reports you filed for these segfaults

I tested mediathekview on fc29. With the missing link, the app start, but when the app windows is closed (for example "about" window), there is a dump. 
(java:28954): Gdk-ERROR **: 19:24:56.159: The program 'java' received an X Window System error.
This probably reflects a bug in the program.
The error was 'BadWindow (invalid Window parameter)'.
  (Details: serial 13349 error_code 3 request_code 20 minor_code 0)
  (Note to programmers: normally, X errors are reported asynchronously;
   that is, you will receive the error a while after causing it.
   To debug your program, run it with the --sync command line
   option to change this behavior. You can then get a meaningful
   backtrace from your debugger if you break on the gdk_x_error() function.)
   
I don't known if it's openjfx or openjdk the problem. I have tested this:
- openjdk-1.8.0_191-b12 with openjfx-8.0.202-b02 -> crash (like described)
- openjdk-1.8.0_191-b12 with openjfx-8.0.191-b10 -> crash
- oracle jdk-1.8.0_202 (early access, release current january 2019) -> ok

Like suggested, please open a new bug for this specific issue.

I get the same bug when I try to execute the JabRef java program
$ java -jar JabRef-4.3.1.jar


Exception in thread "main" java.lang.reflect.InvocationTargetException
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at sun.launcher.LauncherHelper$FXHelper.main(LauncherHelper.java:767)
Caused by: java.lang.RuntimeException: java.lang.UnsatisfiedLinkError: Can't load library: /usr/lib/jvm/java-1.8.0-openjdk-1.8.0.191.b12-11.fc29.x86_64/jre/lib/amd64/libglassgtk2.so
	at com.sun.javafx.tk.quantum.QuantumToolkit.startup(QuantumToolkit.java:267)
	at com.sun.javafx.application.PlatformImpl.startup(PlatformImpl.java:211)
	at com.sun.javafx.application.LauncherImpl.startToolkit(LauncherImpl.java:675)
	at com.sun.javafx.application.LauncherImpl.launchApplicationWithArgs(LauncherImpl.java:337)
	at com.sun.javafx.application.LauncherImpl.launchApplication(LauncherImpl.java:328)
	... 5 more
Caused by: java.lang.UnsatisfiedLinkError: Can't load library: /usr/lib/jvm/java-1.8.0-openjdk-1.8.0.191.b12-11.fc29.x86_64/jre/lib/amd64/libglassgtk2.so
	at java.lang.ClassLoader.loadLibrary(ClassLoader.java:1827)
	at java.lang.Runtime.load0(Runtime.java:809)
	at java.lang.System.load(System.java:1086)
	at com.sun.glass.utils.NativeLibLoader.loadLibraryFullPath(NativeLibLoader.java:201)
	at com.sun.glass.utils.NativeLibLoader.loadLibraryInternal(NativeLibLoader.java:94)
	at com.sun.glass.utils.NativeLibLoader.loadLibrary(NativeLibLoader.java:39)
	at com.sun.glass.ui.gtk.GtkApplication.lambda$new$5(GtkApplication.java:151)
	at java.security.AccessController.doPrivileged(Native Method)
	at com.sun.glass.ui.gtk.GtkApplication.<init>(GtkApplication.java:140)
	at com.sun.glass.ui.gtk.GtkPlatformFactory.createApplication(GtkPlatformFactory.java:41)
	at com.sun.glass.ui.Application.run(Application.java:146)
	at com.sun.javafx.tk.quantum.QuantumToolkit.startup(QuantumToolkit.java:257)
	... 9 more

java-1.8.0-openjdk-1.8.0.191.b13-0.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-2019-9625176922

For the segfaults with MediathekView, please fill a new bug report. I'm investigating on that and it seems that is libglassgtk2.so the source of the problem. There is a bug when JavaFX and Swing are mixed, I see also these segfaults with javafx apps launched with icedtea-web (javaws)

java-1.8.0-openjdk-1.8.0.191.b13-0.fc28 has been pushed to the Fedora 28 stable repository. If problems still persist, please make note of it in this bug report.