As an update, I did actually experience some shifting in really high winds. Not when driving but when parked overnight. It was a little unsettling to discover, but it still felt solidly clamped, and I didn't have any issues subsequently driving 80mph on the highway for five hours. ?♂️
I had a system fault error (or something like that) on day 2 of owning my Gen 2 R1S. They swapped out the front drive unit, no issues since. That was about 6 months ago.
I have a Yakima SkyBox that I had been using with my Mazda CX-9, but now switched over to my R1S. The SkyBox clamp initially wouldn't close on the beefier Rivian crossbars. I replaced the hex bolts on the clamps with ones 1/2" longer and now they clamp on fine.