internal_transactions_sharded_from_mongod.js uses different sessions within the same FSM thread, and its logic requires read-your-own-writes guarantees even across different sessions.
The way the test implements is flawed and does not conform to the specifications.

Therefore, verifyDocuments should use a causal consistent session and call 'advanceClusterTime(max cluster time of this.sessions)' and advanceOperationTime(max operation time of this.sessions). The bumpClusterTime should then be removed altogether.