The db hash and validation check for a ReplSetTest involves running listCollections and collStats commands against each mongod while it is fsync locked. On a mongod with replica set endpoint enabled, those collStats commands are handled using the router code paths which may trigger a catatlog cache refresh. The router service on mongod currently uses the ShardServerCatalogCacheLoader (SERVER-82588). So when a refresh occurs, it requires doing a noop write which will then deadlock since the mongod is fsync locked. This deadlock should go away after SERVER-82588. For now, SERVER-81968 has temporarily changed the number of nodes in the replica sets in the noPassthrough/rs_endpoint/ tests with user collections to 1 to avoid the db hash check. 

The CheckReplHash hook in replica set endpoint suites appeared to suffer from the same hang issue so it has been disabled from all those suites.