Onlyoffice with NextCloud Hub and empty documents


i installed some days ago NextCloud HUB on Debian10 to use integrated Onlyoffice.

Evering works fine. No problems during installation. I was able to start Onlyoffice. I did create some Documents (*xlsx). I was also able to open the Documents on other PCs.
At least i did create a Rsync-Backup from the Data Folder ( /var/www/nextcloud/data) to have my created documentes save.
BUT - if im trying to open the backuped Document (*xlsx) the document are empty. MS Excel is opening and showing a table witout any entries.
I tried to open the same files with Onlyoffice desktop edition - the same again. no entries in documents. But on the NextCloud/Onlycloud Server i can see all entries!

What is wrong here? Any Idea?

Thanks for the answers in adavence.

You are not alone with similar problems

thanks for briefing me.