Multiple times with multiple groups, mob keeps a stack as if an add is up when there isn't one. When engaged, the stack remains even when killing new adds. The stack causes all of the complications it would normally cause, but you can't get rid of it. The only way we found to resolve the issue is to engage the mob, evac, and come back. 100% sure the assistants are gone when this occurs. This happens often enough that it is probably pretty easy to reproduce. I think it has happened in both H1 and H2. I know it can be hard to accept the passing of a dedicated research assistant, but someone really needs to bring The Delving Departed to the acceptance phase of the grief process, please.