I am having the same issue with this file that I created:
I had the file open in front of me, clicked to another tab, came back and got this error:

I have checked all drafts, trash and recent. None of my other 2 team members can access it, nor is it in their trash or drafts.
Since this file is locked and owned by me, it should not have disappeared. Could a Figma staff member please help escalate or check backend recovery? I really need to access it today.
Thank you!