We had a process model (and corresponding tempo action) completely disappear fro

Check /logs/deletion.log

Agreed, check the deletion log. Sounds like it was blown away.

thanks. I found it in the deletion log - now what?

Figure out who deleted it (see last column) and give them a good talking to. Import your backup.

and why was it in the deletion log if I didn't delete it?

Does someone know your credentials to the system? You could attempt to cross reference to the user-request-audit.csv log at the time it happened. That log has an IP address associated with it which you could check to your IP address. Although not 100% it might give you an idea of whether or not YOU actually deleted it or someone logged in as you deleted it.

so...it was deleted by the [Administrator]. Nobody on our team uses that login and every other deletion has a username that we use attached to it. Is there any scenario where something in the system would delete all process models within a folder and assign the deletion to the Administrator?

Interesting, might still be worth an attempted cross check based on time to the user-request-audit log and see if someone logged in as Administrator, could potentially trace to the computer that did it from the IP (once again not fool proof). Another thing to check is if you have any plugins that allow the programmatic deletion of a process model, potentially someone accidentally used that and blew it away? I can not think of a Scenario where Appian would just blow away all process models within a folder.