You can also try todays beta release of Lexicon, it has several fixes that might help here. To try the beta, go into the Lexicon settings and change the Release Branch setting to beta.
The weird thing is some of the songs I was trying to add have been added just a week ago. Don’t know what has changed since then but now they won’t add.
And if you find one of the files from the log on your computer, does it exist?
For example, this one: /Users/briand/Desktop/Music/Tech House/2022/Deeper Purpose - Fantasy (Extended Mix).mp3