From the multitude of videos I've been checking out all over the place, the issue seems to be most prevalent on the left side (the side with the volume buttons) and down in the seam/crack between the two bands. People doing videos showing contact on the right side (the side with the microSIM slot) don't appear to have issues
however, if they switch hands and then make that connection on the left side in that seam bridging those two points wham, the signal chokes.
I know some folks are saying it's just a signal display issue, it's not actually doing anything even in spite of the signal indicator fluctuating so drastically, but when I see the phone disconnect and lose service, well... damned straight that's a design/functionality problem.
The one video with the guy not moving the phone but just applying light finger pressure on that specific seam on the lower left side bridging those two surfaces was more than enough to say "Oh crap, that's a problem..." for me. I've been a licensed Ham radio operator for over 30+ years and when I heard about the new iPhone's design and how they intended to use the actual chassis/frame for the signal propagation, my first instinct was "Oh, no, that's not gonna work, Steve..." but, it's not like he's gonna answer my emails.
It's a big pooch screw and I for one am absolutely confident Apple knew/knows about it - the past iPhones never saw Apple selling their own branded/first-party cases, and now they are with the "bumper" ones.
This wasn't a mistake, it was planned and it's all part of the same money making machine.
"That's my story and I'm stickin' to it..."