Why did some of my iCloud files lose their data?

A couple of months ago, I moved my files from Dropbox to iCloud and synced them from my computer to the iCloud. Today I found that one folder—amongst several—still contains all the files, but they are all empty. The files appear, they have the title and software index (.logicx, .pages, etc.), but they all show the filing coating "Zero bytes."

I was using some of these files only a few days ago. Without proof, I suspect this occurred with the recent upgrade to Ventura. My iCloud account shows the same information from web view and on phone.

Backup: Yes I usually have a back up, but it was unplugged during the past month due to use of other equipment in that USB port. So I don't have back up of the new files.

Can anyone help?