I have a similar problem:
Love my 2021 MYP but over the past five months, I've had this strange and unfortunate problem: whenever I drive over 70 mph, within ~10 minutes, my perfectly-working MYP errors out and I lose regenerative breaking, traction control, stability control, etc. All of this all at once. I have to...
teslamotorsclub.com
It is triggered consistently by drive at 74mph or faster, TACC use doesn't matter. I have stock summer tires on my MYP. Service Center had it yesterday and thought they fixed it after tweaking steering wheel alignment and closed the ticket but of course on the way home I took on the highway and it happened again. I rebooked an appointment but it's not for 2 weeks. Tesla Customer Service... we'll see how it goes.
If your SC fixes this, please share with us so we can guide our local SC better.