According to your screen shots, your 31-6 session is hanging with a Mount Request. This will stay like this forever, if you were to allow it. The bad part is that the 2 mount requests are each tying on at least one drive (maybe more) and Drive licenses
Right-click on these sessions, and pick 'Cancel Device', or if you now have enough media in the Media pool to write to, click Confirm Mount Request and the backup will continue
You also have 2 sessions queueing, I don't know if they are waiting of the Devices, it seems like they would have timed out by now. I might want to right click on these sessions, and Abort the session before dealing with the Mount Requests