We are experiencing this, too. We have Workfront set to time out after 30 minutes of inactivity, but there's no way to set a time for ProofHQ and they don't seem to be recognizing each other. The timing seems random as well.

Once someone is included on a Workfront updates thread, they are there for life. We need to be able to remove people who are no longer on projects or who were tagged in by accident.

It is a huge security risk not to be able to globally delete someone from proofs on which they are the creator. When you hire seasonal contractors, there must be a way to quickly delete them when their contract is up.