trouble with xlsx doc

I have a excel document, with a sheet that is supposed to be locked and blank to unauthorized users.

I opened it with Libreoffice and I am able to “unprotect” the sheet, but it is still blank.

Any ideas?

Is the document delivering its results as expected?
Did you look for content outside of the view (Ctrl+End or Ctrl+Pos1)?
If you don’t find any content in that sheet: What happens if you enter content here and there?
What happens if you delete the sheet?
…Just play around - and do not save the crippled document to the old file