My .calc files appear empty when I open them

I can see my .calc files on the main browser, but when I open them they appear completely empty.

Here I add a link to some images that I’ve taken, that show what I’m seeing. I can view files on the browser; .calc files appear empty when opening, rest of the files open correctly:

I appreciate in advance any help you can provide, please.

(Don’t know if it makes a difference, but I’m using NextCloud via Disroot mail service)