There are a few places in op_observer_impl.cpp and oplog.cpp that call

LastWriteOptimeTs or saveTxnProgress if a session exists on the operation context, but they should instead check the operation context has a transaction number, because the session's state isn't loaded without one.

SERVER-30281 adds invariants that _txnRecord has been set when some of these methods are called, so they will start to fail in the fuzzer.