The jstests/libs/read_committed_lib.js and jstests/sharding/read_committed_lookup.js tests run operations using Database objects associated to two different Mongo objects:

• Some operations use db which is associated to the router's Mongo object.
• Other operations use secondary.getDB(db.getName()) which is associated to a replica set secondary's Mongo object.

As a consequence, some operations that are expected to be causally consistent are concurrent in logical time and fail to produce the expected results. In particular, the operations introduced by SERVER-91703 are concurrent with other operations and the test can still fail under the config server stepdown test suites.

Ensure causal consistency by using the same session for all operations (i.e. use db everywhere).