If its not hardware failure or botched firmware on your R3, then I'm running out of ideas. This one's a bit of a stretch but may be worth trying:
Have you tried testing KA band performance with the R3 mounted immediately to the right of the rearview mirror? I ask because the Classic MS had a metallic layer embedded in the windshield--it was designed to reject heat (and did so very well) but came with the side effect of killing almost all RF signal transmission (
e.g., toll tags wouldn't scan). The entire windshield except for the area immediately to the right of the rearview mirror had that metallic film.
My understanding is that they've moved away from the metallic film in favor of ceramic particles embedded in the windscreen (that has been the case for every M3 and MY I've seen). The ceramic, while better than the metallic film, supposedly still blocks some of the RF passing through the windshield. That's likely why Tesla recommends placing toll tags in the blue area depicted in the image below:
View attachment 958544
For what its worth, between a M3, MY, and MS, the blue area is the location I've always mounted my R3. And performance has been stellar (in line with Vortex Radar's testing) for all three vehicle types.