Description of problem:
  
Mon crashed on changing Cluster Ip subnet on the OSDs. The Cluster Ip was wrongly configured on the OSDs, so the ceph.conf on the MoN abd the OSDs were having different Cluster IP subnets.
On changing the Cluster IP subnet on the OSDs to match that on the Mon , and restarting all OSDs, the primary MON crashed.
No other MONs crashed.

Version-Release number of selected component (if applicable):
ceph version 14.2.8-50.el7cp

How reproducible:
observed only once



 ~]# ceph crash info 2020-09-23_06:19:50.288218Z_967aefe7-4aec-440e-9176-e0d6cb588206
{
    "os_version_id": "7.8", 
    "utsname_release": "3.10.0-1127.19.1.el7.x86_64", 
    "os_name": "Red Hat Enterprise Linux Server", 
    "entity_name": "mon.f03-h02-000-r620", 
    "timestamp": "2020-09-23 06:19:50.288218Z", 
    "process_name": "ceph-mon", 
    "utsname_machine": "x86_64", 
    "utsname_sysname": "Linux", 
    "os_version": "7.8 (Maipo)", 
    "os_id": "rhel", 
    "utsname_version": "#1 SMP Tue Aug 11 19:12:04 EDT 2020", 
    "backtrace": [
        "(()+0xf630) [0x7f05da68c630]", 
        "(std::_Rb_tree_rebalance_for_erase(std::_Rb_tree_node_base*, std::_Rb_tree_node_base&)+0x184) [0x7f05d9da55a4]", 
        "(std::_Rb_tree<int, std::pair<int const, failure_reporter_t>, std::_Select1st<std::pair<int const, failure_reporter_t> >, std::less<int>, std::allocator<std::pair<int const, failure_reporter_t> > >::_M_erase_aux(std::_Rb_tree_const_iterator<std::pair<int const, failure_reporter_t> >)+0x15) [0x555967fc3a25]", 
        "(OSDMonitor::check_failure(utime_t, int, failure_info_t&)+0x951) [0x555967f51101]", 
        "(OSDMonitor::check_failures(utime_t)+0x61) [0x555967f516c1]", 
        "(OSDMonitor::tick()+0x1aa) [0x555967f7a3ea]", 
        "(Monitor::tick()+0x120) [0x555967e437e0]", 
        "(C_MonContext::finish(int)+0x39) [0x555967e1f3b9]", 
        "(Context::complete(int)+0x9) [0x555967e59e99]", 
        "(SafeTimer::timer_thread()+0x180) [0x7f05dd969290]", 
        "(SafeTimerThread::entry()+0xd) [0x7f05dd96aafd]", 
        "(()+0x7ea5) [0x7f05da684ea5]", 
        "(clone()+0x6d) [0x7f05d95488dd]"
    ], 
    "utsname_hostname": "f03-h02-000-r620.rdu2.scalelab.redhat.com", 
    "crash_id": "2020-09-23_06:19:50.288218Z_967aefe7-4aec-440e-9176-e0d6cb588206", 
    "ceph_version": "14.2.8-50.el7cp"
}