The lock file could not be created for exclusive access by LibreOffice, due to missing permission to create a lock file on that file location or lack of free disk space

On opening a saved file in both Calc and Writer I receive the lock file message, since upgrading to version this afternoon.
My files are saved in a D:\My Files folder and this has been edited in the Tools>Options>LibreOffice -Paths - My Documents entry as suggested from the previous answer to this issue. No change, still receiving the error message.

See this FAQ.

Windows Defender is turned off (using AVG)

Did you try disabling AVG?

So far, the above instructions are not working-AVG off. HP Laptop + Win 10 LIbreOffice Version: (x64) as well as 6.4 which I deleted in favor of going back to 6.3 versions since 6.4 is where this issue started.

I uninstalled the LibraOffice and re-installed it to the D: drive where I store my documents and spreadsheets. So far, all seems good and the original files can be opened, edited and saved again with no messages about a Lock File.

Using the Windows File Explorer go to your D:\My Files folder click on view and put a check mark next to hidden items then look for the ~.lock file and delete it.
If this helps then please tick the answer (:heavy_check_mark:) …and/or show you like it with an uptick (∧)

Hidden Items was already checked, there were no ~.lock files found there.

I have the same problem. The ~.lock is not present. Workaround is to save file with another name and delete origin file.

I’ve had this a couple of times and in my opinion, it means the file you are trying to access is not on your drive.
For example, suppose you receive a file by email, you send it to LO, open it, work on it and then save it to your drive as a .docx or whatever.
If you decide to look at it again and choose the file from the ‘recent’ list, the file it will try to open is the one one that you received which is still in the mail library and you will get the above message.
If you navigate to the copy you saved on your drive then it should open without a problem.
this is a very common thing to do as you assume the ‘recent’ copy is the one you saved.
There may well be other examples where you are trying to open a document that is locked in another program somewhere, and you will tell by hovering the mouse and checking the full path to see where it is.
Hope that helps

Mike Kaganski has the right general answer, anti-virus is blocking. Now AVG (and Avast) have similar blocking called Ransomware Protection (or Shield). The user has AVG but rather than turning it off needs to have it on so that AVG Ransomware Protection can ask whether or not to block the application. Alternatively, the user can open AVG, go to the Blocked/Allowed Apps tab and Allow LO