Crash report: "m_pending_event == NULL", f=0x746fb5 "LogCollationClientSM.cc", l=203

Program terminated with signal 6, Aborted.
#0  0x00002ab83c300935 in raise () from /lib64/libc.so.6
(gdb) bt
#0  0x00002ab83c300935 in raise () from /lib64/libc.so.6
#1  0x00002ab83c301db6 in abort () from /lib64/libc.so.6
#2  0x00002ab83a1165f8 in ink_die_die_die (retval=1) at ink_error.cc:43
#3  0x00002ab83a1166ca in ink_fatal_va(int, const char *, typedef __va_list_tag __va_list_tag *) (return_code=1, 
    message_format=0x2ab84690b4e0 "LogCollationClientSM.cc:203: failed assert `m_pending_event == NULL`", ap=0x2ab84690b3e0)
    at ink_error.cc:65
#4  0x00002ab83a116795 in ink_fatal (return_code=1, 
    message_format=0x2ab84690b4e0 "LogCollationClientSM.cc:203: failed assert `m_pending_event == NULL`") at ink_error.cc:73
#5  0x00002ab83a11524e in _ink_assert (a=0x74722b "m_pending_event == NULL", f=0x746fb5 "LogCollationClientSM.cc", l=203)
    at ink_assert.cc:44
#6  0x000000000060d330 in LogCollationClientSM::send (this=0x2ab843c2b980, log_buffer=0x2ab8407a4410) at LogCollationClientSM.cc:203
#7  0x000000000060c14c in LogHost::write (this=0x2ab843c39bc0, lb=0x2ab840849bd0, to_disk=0x2ab84690bcc8, to_net=0x2ab84690bcc0, 
    to_pipe=0x2ab84690bcb8) at LogConfigCollation.cc:243
#8  0x000000000060a054 in LogHostList::write (this=0x2ab843bbcd50, lb=0x2ab840849bd0, to_disk=0x2ab84690bcc8, to_net=0x2ab84690bcc0, 
    to_pipe=0x2ab84690bcb8) at LogHost.cc:380
#9  0x0000000000600db4 in LogBufferManager::flush_buffers (this=0x2ab843bbcdb8, sink=0x2ab843bbcd50, to_disk=0x2ab84690bcc8, 
    to_net=0x2ab84690bcc0, to_pipe=0x2ab84690bcb8) at LogObject.cc:65
#10 0x00000000005eb2ed in LogObject::flush_buffers (this=0x2ab843bbcd20, to_disk=0x2ab84690bcc8, to_net=0x2ab84690bcc0, 
    to_pipe=0x2ab84690bcb8) at LogObject.h:169
#11 0x0000000000604cf8 in LogObjectManager::flush_buffers (this=0x2ab843bd3fa0, to_disk=0x2ab84690bcc8, to_net=0x2ab84690bcc0, 
    to_pipe=0x2ab84690bcb8) at LogObject.cc:1170
#12 0x00000000005e9ca9 in Log::flush_thread_main (args=0x0) at Log.cc:1132
#13 0x00000000005eb4db in LoggingFlushContinuation::mainEvent (this=0x2ab840cb6200, event=1, data=0xfd4fa0) at Log.cc:272
#14 0x00000000004ea432 in Continuation::handleEvent (this=0x2ab840cb6200, event=1, data=0xfd4fa0)
    at ../iocore/eventsystem/I_Continuation.h:146
#15 0x00000000006ffe4d in EThread::execute (this=0x2ab84670b010) at UnixEThread.cc:287
#16 0x00000000006fe832 in spawn_thread_internal (a=0x2ab840cbedd0) at Thread.cc:88
#17 0x00002ab83a358d4c in start_thread () from /lib64/libpthread.so.0
#18 0x00002ab83c3a540d in clone () from /lib64/libc.so.6