Update on testing and results.
I added songs back by artist, e.g., all songs from AC/DC (13 total), launch Rocksmith, attempt to load and play a song without an issue. Quit, add back all songs from The Allman Brothers (5 total), launch... etc. Lather, rinse repeat.
Observations:
For some reason I can't identify, loading Frank Zappa songs (6 total) causes a fail immediately upon launch and load of DLC in the game.
I was able to get a total of 507 CLDC songs loaded, along with 412 ODLC (Steam shows 507, could be song packs for the delta) before the failure would return (aside from not being able to load Zappa).
This configuration worked fairly flawlessly, except one ODLC track (sloe gin, Joe B.) would fail to load the tab/track after clicking on "Play" on the song.
Replaced the .psarc song files from an ODLC back up and that was resolved.
Loading "Stone In Love" by Journey (CDLC) caused the problem to return. And go back to worst case failure state observed, which is after removing all CDLC, some ODLC songs would still fail to load or play in the game.
Deleted the entire Rocksmith Directory from "common" and unzipped my back up from the start of my testing.
Back to the standard game play with no patch nor CDLC.
Next test is to patch the game and load CDLC only in groups of songs I want to work on for the "sessions" ahead. Then swap to a different group once reaching whatever mastery or boredom level feels right.
If the testing of the groups works without issue, I will (eventually) go back to loading larger sets of songs and testing again. But I need to get some playing in for now.
Is this an edge case issue? Or has anyone else run into this and found the root cause or a possible patch or solution?
Cheers all.