The concurrency_sharded_initial_sync.yml test suite preferentially targets reads to the node which underwent initial sync because the initial sync node is the most susceptible to application-level inconsistencies. However this setting only takes effect for the $config.setup() and $config.teardown() functions which run in the main thread. In particular, the setting won't take effect for any of the $config.states functions run by the FSM worker threads.

{mode: "secondaryPreferred", tags: [{tag: "INIT_SYNC"}, {}]}

We should have the concurrency_sharded_initial_sync.yml test suite enable causal consistency (e.g. by setting TestData.runningWithCausalConsistency = true) and import the set_read_preference_secondary.js override file in each FSM worker thread.