Progress of editing a document is not saved

System: Linux 4.15.0-122-generic x86_64
Prozessor: Intel(R) Xeon(R) CPU E5-2650 v2 @ 2.60GHz (8 cores)
Ram: 7.67 GB

Nextcloud: 19.0.4
Type: mysql
Version: 5.7.32
Size: 81,4 MB

Collabora Online - Built-in CODE Server: 6.4.806
Collabora Online: 3.8.2

So I have an odd problem. The collabora webfrontend works fine with good perfomance.
After editing various document formats .odt, .doc, .docx, .ods, .xls, .xlsx, .odp, .ppt or .pptx a lot of content is lost after quitting the webfront end, even thou I save changes via the save-icon. Some changes are saved some changes are not. I tried different timings writing and saving, but I could not find any working and not working patterns. The most changes are saved when I leave the document opened up in a browser tab for a longer period of time + 2 min.
This problem appears in new files as well in existing files.

Saving/editing documents via smb or in home folder synced via Nextcloud Desktop Client work 100 %. Changes made via Libreoffice Desktop Suite appear in the webfrontend after refreshing.

I have a problem same with you, I try everyway but not fix, If you can fix it, Please let me know