I'm running on Windows7, and the Task Manager showed that Thunderbird wasn't running... when I tried to close it I got a Windows message that a subroutine/program was running in the background... so I took the option to end that program. When I restarted Thunderbird, I had a gap in my inbox from 7/2/2013 to 10/4/2016.... and the messages were nowhere to be found.... I also updated Thunderbird today , after noticing the problem...

Any suggestions as to where the messages might have gone?