With the CQF FF enabled, some queries in jstests/core/txns/prepare_conflict.js and jstests/core/txns/timestamped_reads_wait_for_prepare_oplog_visibility.js time out. I've seen this issue on causally_consistent_jscore_txns_passthrough variant and jsCore_txns variant respectively. The tests both mention something along the lines of "Snapshot reads should succeed on non-conflicting documents while a transaction is in prepare", but the reads are hanging.

Examples: Here and Here

Note in one case the query times out, while in the other the test times out. I think this is because only one of the tests added maxTimeMs to queries.