Got Nokian Hakkapeliitta R3s installed on my 18" Aero wheels a few weeks back. I noticed the limited regen right away and thought it odd, but attributed it to the cold weather limited regen at first. Then we had a day that was +18C and still limited/no regen so I started paying more attention. I did a reset of the computer, tried turning regen from std to low and back again; nothing helped. I also started to notice that at slow speeds the regen seemed normal but at normal in-town and highway speeds no regen. I was thinking of asking if anyone else has noticed this behaviour, so thanks for starting this thread. Sounds like my car's behaviour is exactly the same as yours.
Since I got my tires swapped at Kal Tire and I'm using my original rims and TPMS sensors, I find it strange that the car knows I've got winter tires on. I could see Tesla programming for limited regen when roads are possibly poor, but why at +18C? And it strikes me as *really* odd that someone who has winter tires gets limited regen, but someone on the same roads in the same conditions, but with all-season (or even performance!) tires would still have regular regen. They'd be the ones far more likely to lose traction from stronger regen. Odd programming decisions. I guess that's what you get when you have Californians coding software for cars in a Canadian winter.