This line:

fassertFailedNoTrace(!"unknown error in OplogCapMaintainerThread");

is not how fassertFailedNoTrace is supposed to be used - it takes a unique error code. This code takes the address of the string literal (which will be non-zero), logically negates that (to get 0), and then passes that to fassertFailedNoTrace which will log the message:

Fatal assertion 0 at src/mongo/db/storage/oplog_cap_maintainer_thread.cpp 90

This is almost certainly not what was intended. I suspect it should be more like:

LOGV2_FATAL_NOTRACE(5184100, "unknown error in OplogCapMaintainerThread");