On stepdown, while the replication coordinator is holding the RSTL lock in exclusive mode, MigrationDestinationManager::onStepDown() is called. This method takes the MigrationDestinationManager::_mutex.

On the other side, MigrationDestinationManager::exitCriticalSection() first takes the same mutex, and later takes the lock hierarchy (here or here) which includes the RSTL lock.

This inverted lock acquisition order can cause a deadlock on stepdown when a migration is interrupted if a particular interleaving occurs.