iTunes/Music Sync Never Finishes

I have personal iTunes library (~50,000 songs) on external SSD. I created new library (using Option+Music app) on MBP 16” (M3 Pro). All 50K+ songs and all (smart and regular) playlist seem to have ported to Music app with no problem, except it took long time (~20 minutes) to “import artwork.” After that was done, I tried to sync new library to my iPhone (12 Pro Max). It seems to work initially until it reaches “Step 4 of 4 Waiting for changes to apply.” It would hang like that until an error message appears stating sync was not successful because sync did not finish…

Has anyone else had this problem? More importantly, has anyone solve this error. I has a Case ID with Apple Support but they are as baffled as I am…they want to elevate my case to their engineering team…which involves taking QuickTime video of sync process…the last time I did this took over two hours…