I receive this message from time to time when attempting to save a document in Writer or Calc. I am in the habit of leaving the app open on my computer even after it goes to sleep. Using Windows 11, LibreOffice version 7.6.7.2. but this has happened on previous versions as well. Usually note this when I have begun working on the computer, make a change in the document and want to save. I find that after closing LibreOffice and opening again, I am able to save the document.
I have noted numerous reports of this problem when doing a general search with varying descriptions of suggested solutions however none have worked for me except closing the application and reopening. I have tried to remember to close the app when done working.