As much as everyone loves a good conspiracy this was clearly a technical bug. When it occurred, it didn't just reset live photos (side note, why would Apple switch to HEIC if they wanted to waste space?), it acted as if the camera app had no access to its settings and was in some sort of 'default' state. The less obvious side effects were that the HDR option didn't show up even if you had it set to, and Portrait Mode would give you introductory text again.
In any case, I've been running 11.2.1 since it was released and I haven't had it happen once. So I can tentatively say it's fixed? Can anyone else confirm?
On the other hand, I have had a new bug on two occasions: I wake up my phone and the flashlight and camera soft buttons simply don't appear. It was launching the camera with these buttons that caused the bug before, so maybe the fix is that if the camera isn't 'ready' it simply won't show the button.
Yep I can confirm this also, as I had posted before my phone would reset live mode and randomly switch over to HEIC. I haven't seen it happen recently, so Apple must have corrected something.