Make OnlyOffice backup opened documents
More information about when OnlyOffice saves documents to NextCloud is in this issue: https://0xacab.org/infrared/platform_wg/docker-onlyoffice-documentserver/issues/2
Just came back from lunch after having my onlyoffice open but not in use for an hour. Checked my local copy of the file I had open in OnlyOffice, and it was still empty.
This means that I now know for sure that OnlyOffice does not save to NextCloud while it still has an open connection to someone. I think it wouldn't hurt if it saved every five minutes or so, just to make sure that if anything happens, document data is not lost.