Same issue happenned to me 2 days ago. My Vault was in OneDrive. When I opened it my folder structure was still there but no data.
My OneDrive recycle bin is empty.
I tried copying a vault from 2 weeks ago - It shows as still copying after 2 days… message - “copying 1 item to My Files 6355100%”.
I did use the sandbox folder 3 days ago but just looked and can’t remember if I even created any files. But I had closed it before this happened.
Can anyone advise on how to get help with Onedrive?