Summary: Excel needed to close. Upon reopening it all the formatting was removed from all tabs. The formulas and links are still there, just all formatted in plain text.

Details: This happened a year ago and it kept happening. Sometimes becuase Excel crashed sometimes just when I opened it. After a while we just copied it all to a new workbook and it was fine.

It just happened with another workbook. We are okay becuase we went to a backup but I am worried that this is going to be a repeating issue again.

Has anyone encountered something like this before? Suggestions for fixing it?

Thank you very much for your help.
Todd