I've attached the test. Here are the logs . Here's the stacktrace: [js_test:initsync_fuzzer-cacf2-1557881965671-05] 2019-05-15T16:43:12.171-0400 d34588| 2019-05-15T16:43:12.171-0400 F - [repl-writer-worker-2] Invariant failure isCrudOpType() src/mongo/db/repl/oplog_entry.cpp 292 [js_test:initsync_fuzzer-cacf2-1557881965671-05] 2019-05-15T16:43:12.171-0400 d34588| 2019-05-15T16:43:12.171-0400 F - [repl-writer-worker-2] [js_test:initsync_fuzzer-cacf2-1557881965671-05] 2019-05-15T16:43:12.171-0400 d34588| [js_test:initsync_fuzzer-cacf2-1557881965671-05] 2019-05-15T16:43:12.172-0400 d34588| ***aborting after invariant() failure [js_test:initsync_fuzzer-cacf2-1557881965671-05] 2019-05-15T16:43:12.172-0400 d34588| [js_test:initsync_fuzzer-cacf2-1557881965671-05] 2019-05-15T16:43:12.172-0400 d34588| [js_test:initsync_fuzzer-cacf2-1557881965671-05] 2019-05-15T16:43:12.172-0400 d34588| 2019-05-15T16:43:12.172-0400 F - [repl-writer-worker-2] Got signal: 6 (Aborted). [js_test:initsync_fuzzer-cacf2-1557881965671-05] 2019-05-15T16:43:12.173-0400 d34588| 0x7faebee287a1 0x7faebee2802e 0x7faebee280cf 0x7faebcc37890 0x7faebc872e97 0x7faebc874801 0x7faebeda8bc6 0x7faebfd07e60 0x7faec1b5e492 0x7faec1b6013a 0x7faec1b6255d 0x7faec1b54de8 0x7faec1b5bffa 0x7faec10cfb16 0x7faec10d0d10 0x7faec10d2755 0x7faebd4b957f 0x7faebcc2c6db 0x7faebc95588f [js_test:initsync_fuzzer-cacf2-1557881965671-05] 2019-05-15T16:43:12.173-0400 d34588| ----- BEGIN BACKTRACE ----- /mnt/home/vlad/mongodb/github/mongo/src/mongo/util/stacktrace_posix.cpp:174:39: mongo::printStackTrace(std::ostream&) /mnt/home/vlad/mongodb/github/mongo/src/mongo/util/signal_handlers_synchronous.cpp:182:20: mongo::(anonymous namespace)::printSignalAndBacktrace(int) /mnt/home/vlad/mongodb/github/mongo/src/mongo/util/signal_handlers_synchronous.cpp:239:28: mongo::(anonymous namespace)::abruptQuit(int) ??:0:0: ?? /build/glibc-OTsEL5/glibc-2.27/signal/../sysdeps/unix/sysv/linux/nptl-signals.h:80:0: __libc_signal_restore_set /build/glibc-OTsEL5/glibc-2.27/signal/../sysdeps/unix/sysv/linux/raise.c:48:0: gsignal /build/glibc-OTsEL5/glibc-2.27/stdlib/abort.c:79:0: abort /mnt/home/vlad/mongodb/github/mongo/src/mongo/util/assert_util.cpp:104:15: mongo::invariantFailed(char const*, char const*, unsigned int) /mnt/home/vlad/mongodb/github/mongo/src/mongo/util/invariant.h:69:33: void mongo::invariantWithLocation<bool>(bool const&, char const*, char const*, unsigned int) /mnt/home/vlad/mongodb/github/mongo/src/mongo/db/repl/oplog_entry.cpp:292:5: mongo::repl::OplogEntry::getIdElement() const [clone .cold.94] /mnt/home/vlad/mongodb/github/mongo/src/mongo/db/repl/sync_tail.cpp:895:53: mongo::repl::SyncTail::getMissingDoc(mongo::OperationContext*, mongo::repl::OplogEntry const&) /mnt/home/vlad/mongodb/github/mongo/src/mongo/db/repl/sync_tail.cpp:951:57: mongo::repl::SyncTail::fetchAndInsertMissingDocument(mongo::OperationContext*, mongo::repl::OplogEntry const&) /mnt/home/vlad/mongodb/github/mongo/src/mongo/db/repl/sync_tail.cpp:1071:58: mongo::repl::multiSyncApply(mongo::OperationContext*, std::vector<mongo::repl::OplogEntry const*, std::allocator<mongo::repl::OplogEntry const*> >*, mongo::repl::SyncTail*, std::vector<mongo::MultikeyPathInfo, std::allocator<mongo::MultikeyPathInfo> >*) /opt/mongodbtoolchain/revisions/e84eb3fd219668197589e62dba14b9914712642d/stow/gcc-v3.ipd/include/c++/8.2.0/bits/std_function.h:283:40: std::_Function_handler<mongo::Status (mongo::OperationContext*, std::vector<mongo::repl::OplogEntry const*, std::allocator<mongo::repl::OplogEntry const*> >*, mongo::repl::SyncTail*, std::vector<mongo::MultikeyPathInfo, std::allocator<mongo::MultikeyPathInfo> >*), mongo::Status (*)(mongo::OperationContext*, std::vector<mongo::repl::OplogEntry const*, std::allocator<mongo::repl::OplogEntry const*> >*, mongo::repl::SyncTail*, std::vector<mongo::MultikeyPathInfo, std::allocator<mongo::MultikeyPathInfo> >*)>::_M_invoke(std::_Any_data const&, mongo::OperationContext*&&, std::vector<mongo::repl::OplogEntry const*, std::allocator<mongo::repl::OplogEntry const*> >*&&, mongo::repl::SyncTail*&&, std::vector<mongo::MultikeyPathInfo, std::allocator<mongo::MultikeyPathInfo> >*&&) /opt/mongodbtoolchain/revisions/e84eb3fd219668197589e62dba14b9914712642d/stow/gcc-v3.ipd/include/c++/8.2.0/bits/std_function.h:687:71: std::function<mongo::Status (mongo::OperationContext*, std::vector<mongo::repl::OplogEntry const*, std::allocator<mongo::repl::OplogEntry const*> >*, mongo::repl::SyncTail*, std::vector<mongo::MultikeyPathInfo, std::allocator<mongo::MultikeyPathInfo> >*)>::operator()(mongo::OperationContext*, std::vector<mongo::repl::OplogEntry const*, std::allocator<mongo::repl::OplogEntry const*> >*, mongo::repl::SyncTail*, std::vector<mongo::MultikeyPathInfo, std::allocator<mongo::MultikeyPathInfo> >*) const /mnt/home/vlad/mongodb/github/mongo/src/mongo/db/repl/sync_tail.cpp:1278:92: operator() /mnt/home/vlad/mongodb/github/mongo/src/mongo/util/interruptible.h:179:47: runWithoutInterruptionExceptAtGlobalShutdown<mongo::repl::SyncTail::_applyOps(std::vector<std::vector<const mongo::repl::OplogEntry*> >&, std::vector<mongo::Status>*, std::vector<std::vector<mongo::MultikeyPathInfo> >*)::<lambda(auto:20)> [with auto:20 = mongo::Status]::<lambda()> > /mnt/home/vlad/mongodb/github/mongo/src/mongo/db/repl/sync_tail.cpp:1277:20: operator()<mongo::Status> /mnt/home/vlad/mongodb/github/mongo/src/mongo/util/functional.h:144:10: callRegularVoid<mongo::repl::SyncTail::_applyOps(std::vector<std::vector<const mongo::repl::OplogEntry*> >&, std::vector<mongo::Status>*, std::vector<std::vector<mongo::MultikeyPathInfo> >*)::<lambda(auto:20)> > /mnt/home/vlad/mongodb/github/mongo/src/mongo/util/functional.h:158:39: _ZZN5mongo15unique_functionIFvNS_6StatusEEE8makeImplIZNS_4repl8SyncTail9_applyOpsERSt6vectorIS7_IPKNS5_10OplogEntryESaISA_EESaISC_EEPS7_IS1_SaIS1_EEPS7_IS7_INS_16MultikeyPathInfoESaISJ_EESaISL_EEEUlT_E_EEDaOSP_EN12SpecificImpl4callEOS1_ /mnt/home/vlad/mongodb/github/mongo/src/mongo/util/functional.h:108:54: mongo::unique_function<void (mongo::Status)>::operator()(mongo::Status) const /mnt/home/vlad/mongodb/github/mongo/src/mongo/util/concurrency/thread_pool.cpp:341:9: mongo::ThreadPool::_doOneTask(std::unique_lock<std::mutex>*) /mnt/home/vlad/mongodb/github/mongo/src/mongo/util/concurrency/thread_pool.cpp:294:19: mongo::ThreadPool::_consumeTasks() /mnt/home/vlad/mongodb/github/mongo/src/mongo/util/concurrency/thread_pool.cpp:247:24: mongo::ThreadPool::_workerThreadBody(mongo::ThreadPool*, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&) ??:0:0: ?? ??:0:0: start_thread /build/glibc-OTsEL5/glibc-2.27/misc/../sysdeps/unix/sysv/linux/x86_64/clone.S:95:0: clone [js_test:initsync_fuzzer-cacf2-1557881965671-05] 2019-05-15T16:43:12.176-0400 d34588| ----- END BACKTRACE -----