Has anyone who's driven a few hundred miles on their new snow tires still experiencing this? I ask because new tires, even snow tires, have a break-in period where you're wearing off the slippery release compound (see
https://blog.tirerack.com/blog/make-driving-fun-2/winter-tire-break-in-v1.
If you're using the same wheels and TPMS sensors, the vehicle has no clue you've changed anything except from its behavior on the road. Roadster V2 & V2.5 have a tire replacement "learn" function that enables the car to recalibrate to the new tire, which might have a different diameter than the tire it's replacing (see
No regen after tire replacement if you're interested).
If traction overall is poor, then regen on RWD cars may cause the rear tires to slip slightly, but since the fronts don't have regen, those wouldn't slip. The resulting difference in tire rotation would be perceived by the vehicle and could be causing the car to reduce regen, just as Traction Control can reduce power under acceleration. With the release compound still on the new tires, that could cause enough additional slip to make regen reduce in situations that a broken-in All Season tire wouldn't.