I’m also seeing what I think is a related issue - I have an administrator view which shows me statistics on Active and Termiated sessions. In the old version, terminated sessions cleaned themselves up after a minute or two.
In 2021 R3.1, they seem to stick around - in this screenshot, every session noted with (X) is one that has been terminated, but still exists:
These “ghost” sessions don’t seem to be causing a big issue, but I imagine they are leaking a little bit of memory (and my app has only been running for about 24 hours - longer term, this would concern me)