Eli Zaretskii <eliz@gnu.org> writes:

> Hmm... but now I see that the previous code already renamed the file
> with the new data after the new data was completely written, is that
> right?  If so, I don't think this last change will help, and we need
> to understand how come rename-file doesn't already solve this problem.

Yes, it is right.
You suggested using write to temporary file -> rename method earlier and
I implemented it.

> Is the file being read and written a regular file or a symlink?

Regular file.

> One thing to try is to let-bind write-region-inhibit-fsync to a nil
> value around the code which writes the data to the org-persist file.
> Maybe we have some tricky race condition between the filesystem
> flushing its buffer after one instance of Emacs wrote the file, and
> the other instance of Emacs that opens the file for reading.

The attached diff does it. Need to test.