I remembered this thread just now when I put my 6S+ in landscape mode (I totally dig on it for using it at my desk), and wondering if you've installed 9.0.2 yet - and most importantly, if it resolved it?
I'm still having a bug that when I try to switch to zoomed mode it doesn't reset the phone. It just makes the screen go dark and the phone non-responsive. I have to manually reset (after which the phone is in zoomed mode). Weird.See above. Me and few other folks had this behavior, i.e., didn't rotate until you touched/tapped (interacted like you said), then it was fine, even though in apps it worked fine.
My solution was to set it to zoom, let it reboot, then set it back to standard, fixed. That trick didn't work for the other folks in this thread having the same issue.