Local Media Assets must be at the top if you want Plex to consider your embedded metadata. It must be there when you add the files into Plex.
Changing the order afterwards doesn’t make a difference indeed.
That little log snippet is unfortunately not enough to diagnose the issue. Please provide the full archive.
I definitely recommend to stay with ID3v2.3 with UTF-16 charset.
Use one album or artist as a test. Change the ID3 tags and perform the Plex Dance with the files.
