I saw this thread before but never really looked into it, thought people were having problems with the login. It started happening to me too like 2 days ago and it keeps doing that, for some reason in the middle of botting, it just stops and the msg I see on my HB window is that the session is invalid. It's good that you are looking into it, it's a major stability issue.
I have finally resolved those God damn black screens by cutting, changing my routes, blacklisting nodes and now this issue slaps me in the face =(