As part of SERVER-84330, transactions_block_ddl.js was unblocked in sharded environments. In sharded environments the rename command here fails (and below in the replica set endpoint case across dbs) because the rename command issued fails NamespaceExists even though the collection is dropped before running the test and the previous call to 'testTimeout' shouldn't create it. Preliminary investigation is in the comments.

To reproduce, unblock the rename on mongos and run the test with the suite sharded_jscore_txns.