Hey everyone, apologies for not updating this thread for a while - life got in the way.
After 47 days in the shop, countless parts replaced and two visits from GM field engineers, I'm happy to say that they finally were able to fix the issue.
Per the writeup I have, the root cause was poor terminal pin tension on the EBCM harness CAN 2 terminals 10/11 and 24/25. They replaced these terminals and it's been running fine ever since.
I never ended up retaining the lawyer. GM did not initially approve a buyback, and I never pressed the issue since they were able to fix my car. Cadillac/GM customer service proactively offered me 50k GM rewards points (equivalent to $500) and to reimburse me for my April payment.