
Go to Deleted files in Dropbox to check if the file or folder exists there.Check your desktop or mobile Dropbox app to check sync errors.
The two quick things to do in this kind of scenario is:
You are not the owner of that file but someone else who shared the file or folder with you revoked the sharing access. The file you are searching for hasn’t got synced due to desktop or mobile client issues. You may have accidentally deleted a file or folder while not paying attention. You may have deleted the file and forgot about it. The following are some of the major reasons. There are several reasons why some Dropbox files go missing in a personal (consumer) account. This isn’t an uncommon problem, and usually, Dropbox isn’t at fault for it in most cases.
Many Dropbox users often find their files or folders go missing. How to Recover Dropbox Files that Were Missing