I would check if there is a lock file for the file you are trying to save. Enable showing hidden files in your file browser or do a ls -la in a terminal window and look for a file like ".~lock.Без имени 1.odt#". If one is present, make sure you close all LibreOffice windows and delete it with your file browser or rm.
These files can get left behind if LibreOffice isn't closed properly.