The UBSAN Enterprise RHEL 8.0 DEBUG build variant currently selects the concurrency tasks to run based on the following Evergreen task tags.

- name: .concurrency !.no_txns !.repl !.kill_terminate

The changes from 542d00d as part of SERVER-39414 had subtly define the concurrency_replication_ubsan, concurrency_replication_causal_consistency_ubsan, concurrency_replication_multi_stmt_txn_ubsan to not have the "repl" Evergreen task tag. The changes from f83d51c as part of SERVER-50710 unknowingly added the "repl" Evergreen task tag to these definitions and caused the UBSan DEBUG build variant to stop running these tasks.

The concurrency_replication_ubsan, concurrency_replication_causal_consistency_ubsan, concurrency_replication_multi_stmt_txn_ubsan tasks were always meant to be temporary. They were first introduced in July 2018 as part of SERVER-35964. However there appeared to be a memory pressure issue which was never investigated. The more recent changes from 38a98af as part of SERVER-35964 removed the Evergreen task definitions and resmoke YAML suite files because they appeared unused.

We should restore the MongoDB 4.4 coverage. We can consider either reintroducing the Evergreen task definitions and resmoke YAML suite files or updating the Evergreen task selector for the build variant.