The JournalFlusher is reading the oplog collection without any collection level locks, so it can run concurrently with a full:true validate command on the same collection. Opening a cursor while validate calls WT:verify will cause a WT EBUSY error, which MongoDB converts into a WriteConflictException. Query normally retries reads when given a WRITE_CONFLICT_RETRY_ONLY yield policy, but for some reason it gets to the retry code and finds a NO_YIELD policy.

SERVER-47959 will temporarily resolve the test failures by retrying at a higher level, until this bug can be tracked down.