SnapshotHelper::shouldReadAtLastApplied is called explicitly from AutoGetCollectionForReadBase and via SnapshotHelper::getNewReadSource. It is checking ReplicationCoordinator::canAcceptWritesForDatabase which can change as we're not holding the RSTL. A different answer would trigger the following fassert: https://github.com/mongodb/mongo/blob/51e3e36ac48cac80c920e5e418013fdb0a6747f2/src/mongo/db/db_raii.cpp#L262-L265