I have a 2018 Model 3 with the FSD beta running v2022.44.30.5, which is the latest version available to me.
I just wanted to weigh in because the emphasis on open desert highway roads in the original post feels very familiar to a recent experience I had. I live in the Minneapolis/St. Paul, MN metro and haven't taken my Model 3 out of the metro area since May, 2021, at which time I took it from the southern metro to western North Dakota, roughly 600 miles, entirely on I-94. That trip in May, 2021 was great, and driving as I do around the Twin Cities on Autopilot and FSD has been overall very good. There's the occasional phantom braking incident but honestly it's very rare and hasn't been much of a concern to me even as I see the headlines.
So then it was very surprising to me when a week and a half ago I made the same drive I did along I-94 up through MN and across ND that I was suddenly experiencing phantom braking quite often, and not in the usual scenarios that I've expected with a poor interpretation of an overpass or a semi hauling an usual load, but mostly in completely open road in perfect driving conditions. This wouldn't have been using FSD since I was on the highway, but in some stretches the car was braking as commonly as every mile or two, and sometimes with up to 10 miles in-between. This made for a very uncomfortable 450 miles driven during the daylight. But I had a break between that first 450 miles where night fell and I drove the last 150 miles in the dark, and had no phantom braking at all. I also noticed that when I was on open road with literally no one else around, at the very edge of the vision on the vehicle display, it would flicker as if it had seen a vehicle even if one wasn't there. Never immediately in front of our vehicle, but just barely on the edge of what it showed. When I got into areas with traffic (read: any vehicles in the ~500 feet in front of me at all) the car would be more stable and phantom braking didn't happen nearly as much.
On the trip back, it was about a 400/200 mile day/night split, and I had a similar experiences with the lack of traffic and nighttime improvements. However, I also noticed we had a lot of mirages on the road in some stretches. North Dakota is essentially a frigid desert, so it was ~15º F but sunny so the pavement warms up and results in mirages even in the winter. I also noticed that it seemed to get tricked by these mirages on the road making it think a vehicle I was following were closer than they were or the road was effectively disappearing at points.
And now that I'm back driving around the Twin Cities, the car is fine again, even at those same 75-80 mph speeds on highways with Autopilot (not FSD).
I actually have an order on a Model Y with a delivery date coming up in about a month. Stopping to charge doesn't bother me and I really have enjoyed my Model 3, so I was looking forward to upgrading. But now I'm not sure if I want to because I'm nervous of this type of experience when I do make long trips more often. It's so strange to me that this trip, which was great 2 years ago, was so uncomfortable and awful now. I really hope Tesla can fix it when they make the FSD highway stack available, or through some other means, whatever that may be. Honestly I'd even settle for the ability to use cruise control in a "dumb" way. I just don't like having to manually drive for so long or be subject to frequent whiplash.