Ods files losing all data - not sure why

In the past 1-2 weeks, I;ve noticed that my spreadsheet files that I edit in next cloud and being wiped clean. No data at a in them. 0KB.

What might cause this?

We are using NC 28.04

You need to give us more to go on.

How do you have Collabora (CODE/CO) deployed? And which version of CODE and the Nextcloud Office app?