difficult to understand this question. Are you saying fm crashes after all the FILES have been closed?
I think you answered your own question. I had similar behaviour resulted by a plugin. You have a plugins cocktail!
Instead of disabling the plugins, try to remove them completely. Check your system after this and if it is OK, add plugins one at a time.
If the plugin are not an issue, this could be a problem with a closing triggered script in one of the files. Again, open and close one file at a time.
Seems like that was the answer. I removed everything from the general extension folder and kept just the ones i know are 64 bit in the 14 folder and crashes have stopped. Tri URL or Activator might be an issue. One client uses NRG software and it installs those. Am working through those version issues. It is surprising but even if the plugins are not loaded and are in the saved folder they seem to cause this crash.