We have a collection with 10 docs, and 2 client threads are operating on it. Each one is repeatedly doing a multi-update on all docs in the collection. The multi-update involves both normal indexes and multikey indexes.

At some point, the server starts logging "[conn5] Got a WriteConflict in the middle of a multi-update, retrying the current doc" over and over, and the clients stop making progress.

Attached are the server log and the backtraces of all threads after attaching gdb to the server.