We just upgraded our Sage 300 Construction and Real EState to 20.3.1 and my Sage Job Cost session just closed when I hit "Finish" to post the entry.  The entry did not post, but I was able to post it through JC post entries.  When running Job Cost reports to the screen, when making a new range to print, the first range does not close.  I have not seen any solutions for these issues posted on this forum yet.

I think I fixed the problem to the session closing without warning.  I unpinnned all the Sage icons on my desktop taskbar, reboot my system, and repinned the Sage icon(s) on the taskbar.  What a difference!

Thank you LMR for responding. I really hope this would fix my issue too.