Identifying hanging threads

If the threads eventually finish, they are not "hanging". I would call them "long-running" threads instead, but will use the term "hanging threads" thereafter to keep it simple.

Generally speaking, if no users are complaining about slow operations, or no significant performance issues are observed, you don't need to worry about those hanging threads. Just let them run their courses. The really worrying hanging threads are those never finish and keep popping up - they will eventually exhaust the thread pool and the server becomes unresponsive.

If however, you want to get to the bottom of it for whatever reason, what you have been doing is the right approach. The user ID associated with the thread is definitely the one initiated the operation (it may even be a background task in the user session), but the actual user may not recognize the operation. For example, if a user adds a member to the project area, the said operation will be triggered, but the user may not realize it. The stack trace should give you good indication of what the user is doing, but if you can't decipher, contact IBM Support.