Why has my Cardboard app suddenly gone wonky?

I've been building Cardboard apps just fine for the last week and a half, but today when I put a fresh build on my iOS 11 phone, I got this:




Note how the images use only about 2/3 of the screen; they used to extend to the full height. This even applies (in fact, even more so) to the thin white dividing line between the views. And note too how the left eye is looking at the right side of the pond, while the right eye is looking at the left side of the pond, at angles so divergent that there is literally nothing that's visible in both views.

I've tried using the gear button to re-select my viewer, scanning the Cardboard icon on the side, but it made no difference. I've quit and restarted the app; no dice. I'm at a loss.

Has anybody seen anything like this before? What could cause it, and how do I fix it?

 

Huzzah! In fact it appears that what was different today, vs. earlier this week, is that my phone today happened to have Orientation Lock on. It didn't even occur to me that that might matter (but it kinda makes sense that it does).

Thank you for clearing this up! I'll look for some way to at least detect the problem, but at least now I know what to do (and what to tell users if they complain).