I have a wireless TrueNAS network server that I access from a number of computers. Up until recently, there weren’t any issues opening and saving LibreWriter documents to it. It seems right after a recent LibreOffice Office update, something broke. I can open a file and edit it, but when I try to save it back I get a save error: “Error creating object. Could not create backup copy.”. I can save the file under a new using Save As… This means every time I edit a file, I have to save it under a different name.
I have LibreOffice 26.2.3.2 running on a Windows 10 Home 64-bit system.
It sounds like an anti virus or anti ransomware issue. You probably need to add soffice.bin to the allowed list of the security software
While an anti-ransom-ware protection is possible the message is quite specific. You should also check, if the option to create backups is active and where they are created. Maybe that partition is full or reached quota:
https://help.libreoffice.org/latest/en-GB/text/shared/guide/doc_autosave.html