Hi sorry about this. There is a bug with the attachment retention detection code which marked recently deleted files that was uploaded a long time ago to be stale and to be collected.
I’m coming up with a fix for this algorithm right now, but unfortunately that does mean the file itself is likely already gone from our side.
If you haven’t done too much work since the accidental deletion, I think the best course of action at this point is to look for a disk-based data recovery tool (I know Recuva is a good one for Windows). There’s a chance your file hasn’t been overwritten yet and a recovery tool would be able to find it intact.
Again, I’m sorry this happened. From our side we will be patching this issue very soon.
Licat has gone through the technical side, I just want to let you know that we’re really sorry for not being able to recover the attachments. We’ll do what we can to make sure it doesn’t happen in the future.
Let us know if you need a refund by DM’ing me. Again I’m really sorry this has happened!