The session.state file has nothing to do with torrents, it's just config. It's a long shot but check the state folder in your config for .bak backup files of torrents.state and torrents.fastresume however they might have already been overwritten
Without any personal backups, I'm afraid not, the original torrent files that were loaded should be in the state folder but obviously without any renaming details.
If it's any consolation, I have been working on preventing this in development code.
I came across this issue recently with dev 189 or possibly just after. I have a script that reloads the active torrents but it would sure be nice to be able to figure out why this is occuring, the logs aren't giving me any clues. I'm running dev200 now, see what happens.
I've been suffering from this issue since I started using Deluge in 2010, and it's still happening in 2020 with 2.0.4.dev38. I run a backup script at the background, but this problem is really annoying.
Hey, just FYI, I enabled your plugin, changed the path, and it crashed deluge. Then when the server restarted, my whole list of torrents was gone. I had no clue this type of crap has been a thing with deluge since it was a baby, as per /viewtopic.php?t=26775&start=110 - so ... yeah. Good job I guess? Maybe one smart thing you could have done is check that the .bak file you're overwriting on startup is not BIGGER than the one you're about to write? But no... why be smart about it? Just wipe people's lists! It's all good. :facepalm: