I have an iOS VOIP app using PJSIP v2.3.0. After the iOS 11 release, I have been seeing a lot of instances of the crash below. I have fabric (crashlytics) integrated with my app and this is the backtrace of the thread that crashed. Crashed: Thread 0 libsystem_kernel.dylib 0x186819348 __pthread_kill + 8 1 libsystem_pthread.dylib 0x18692d354 pthread_kill$VARIANT$mp + 396 2 libsystem_c.dylib 0x186788fd8 abort + 140 3 libsystem_c.dylib 0x18675cabc basename_r + 314 4 MyApp 0x101a2ab58 pj_sockaddr_get_port + 10115892 5 MyApp 0x101a24e28 udp_on_read_complete + 10092036 6 MyApp 0x1019bba74 ioqueue_dispatch_read_event + 9661008 7 MyApp 0x1019bd1f0 pj_ioqueue_poll + 9667020 8 MyApp 0x101a08788 pjsip_endpt_handle_events2 + 9975652 9 MyApp 0x1019df334 worker_thread + 9806608 10 MyApp 0x1019cf274 thread_main + 9740880 11 libsystem_pthread.dylib 0x18692c32c _pthread_body + 308 12 libsystem_pthread.dylib 0x18692c1f8 _pthread_body + 310 13 libsystem_pthread.dylib 0x18692ac38 thread_start + 4 The thread crashes due to assertion on pj_sockaddr_get_port PJ_ASSERT_RETURN(a->addr.sa_family == PJ_AF_INET || a->addr.sa_family == PJ_AF_INET6, (pj_uint16_t)0xFFFF); Note : PJ_ENABLE_EXTRA_CHECK is defined 0 for my app so PJ_ASSERT_RETURN is simply PJ_ASSERT here. The PJSIP logs leading upto this crash tells something interesting. The app is backgrounded and it unregisters. When the app is brought to foreground after several minutes it tries to register. I see the following warning messages and at the same time crashlytics reported the crash mentioned above with the backtrace. 2017-09-28 21:00:11 TID=50691 [pjsua] Log Level-1 : 16:00:11.267 ioq_select Error replacing socket: Invalid argument 2017-09-28 21:00:11 TID=50691 [pjsua] Log Level-1 : 16:00:11.267 udp0x10de7f3a0 Warning: pj_ioqueue_recvfrom: [err 120009] Bad file descriptor 2017-09-28 21:00:11 TID=50691 [pjsua] Log Level-1 : 16:00:11.267 udp0x10de7f3a0 Warning: pj_ioqueue_recvfrom: [err 120009] Bad file descriptor . . . 2017-09-28 21:00:18 TID=50691 [pjsua] Log Level-1 : 16:00:15.256 udp0x10de7f3a0 Warning: pj_ioqueue_recvfrom: [err 120057] Socket is not connected 2017-09-28 21:00:18 TID=50691 [pjsua] Log Level-1 : 16:00:15.256 udp0x10de7f3a0 Warning: pj_ioqueue_recvfrom: [err 120057] Socket is not connected 2017-09-28 21:00:18 TID=50691 [pjsua] Log Level-1 : 16:00:15.256 udp0x10de7f3a0 Warning: pj_ioqueue_recvfrom: [err 120057] Socket is not connected . . . 2017-09-28 21:00:18 TID=50691 [pjsua] Log Level-1 : 16:00:18.262 udp0x10de7f3a0 Warning: pj_ioqueue_recvfrom: [err 120038] Socket operation on non-socket 2017-09-28 21:00:18 TID=50691 [pjsua] Log Level-1 : 16:00:18.262 udp0x10de7f3a0 Warning: pj_ioqueue_recvfrom: [err 120038] Socket operation on non-socket 2017-09-28 21:00:18 TID=50691 [pjsua] Log Level-1 : 16:00:18.262 udp0x10de7f3a0 Warning: pj_ioqueue_recvfrom: [err 120038] Socket operation on non-socket These warning messages appear because of spinning loop inside udp_on_read_complete from what I understand. Could iOS be re-claiming the socket that pjsip is trying to use? Did anybody come across this crash? Any kind of pointers/guide is most welcome. Thanks