Well, as of mid -January I did an 8 hour round trip and used Autopilot with Auto-Steer for about 6 of those hours. I didn't have one phantom braking. Now mind you this was on a trip from Los Angeles to Las Vegas, and the return trip two days later.
The only time it braked, and it caught me off guard was a semi started drifting in my lane and I hadn't noticed it, but the AP had.
I used to have a point on my commute that would occasionally cause the phantom braking, but that one seems to have been fixed. It involved going through a small tunnel (overhead), and it got my attention the first time it happened. Now I don't even think about it, it goes right through it.
YMMV, but as I said, I use it with Auto-steer almost 90% of the time.