RecoverableCriticalSectionService intends to keep an in-memory state whose state mirrors the critical sections that are durably persisted on a collection. Currently, on startup, we initialize this in-memory state by hooking into ReplicaSetAwareService's onStartup method and then reading from the collection. On steady state replication an opObserver keeps it in sync.
However, ReplicaSetAwareService::onStartup is not the correct place to do such initialization, because by the time it gets called initialSync and startupRecovery have not run yet. This can cause a freshly started up shard to miss an in-memory critical section.