Hi ,
Thank you for your explanation and advice. It helped when I have deleted lock files as you said so I was happy with that.Sometimes was still the same but I have repeated the lock file delete process and was fine.
I am sorry I did not have time to come back and report.
Since few mounts I do not have this issue any more. Probably because I have a newer version of OnlyOffice which for now is ONLYOFFICE Desktop Editors Community version 9.2.1.43 (x64 flatpak) where the problem is resolved.