I have a similar problem. The "post covering" as you refer to it, hasn't exactly come loose, but I've noticed a gap of about a half inch between the decorative trim and the actual structural element. When I press on the trim, I can close that gap, but as soon as I release the pressure, the gap reappears. I just noticed it about a month ago. I bought the car in September of 2020 and am not sure if it was there to begin with or happened because I kept brushing up against it as I got in and out of the car. I haven't contacted Tesla yet, but I will at some point. In the meantime, I now get in the car ass first, sitting down on the seat and then swiveling my legs into the car. That avoids any contact with the post.