I have a game in development, and all has been progressing well for the last six months or so. It's been running at a smooth 60fps on all our test devices (iPhone 5s, iPad Air 2, iPod 6gen, and two iPhone 6s's). There is no level-of-detail system in place yet; all devices are showing the exact same content. It's using GLES2.0 with a handful of simple vertex and pixel shaders; nothing complicated or unusual.
Then we updated the two 6s's to 10.3.3, and the framerate instantly more than halved to 20-30fps. No changes to the game; the exact same build that still ran at 60fps on a 5s now chugs and stutters along on a 6s under iOS 10.3.3.
Obviously I went straight to the debugger and profiling tools. Absolutely no help. No extra errors or warnings from the debugger, and the profiler showed no anomalies. To be more specific, the profiler showed the same PROPORTION of time spent doing the same things across all devices, but on the 6s it showed around half the CPU utilisation, almost as if it were deliberately throttling back.
I learned about the battery 'fix' in 10.x that causes some 6s's to throttle regardless of the 'low power' setting, However neither phone exhibits slowdown running other (much more demanding) game apps, and they both give GeekBench results in line with what you would expect. Neither serial number is eligible for the battery replacement program.
Last night I finally allowed the iPod 6gen to update itself to iOS 11. I left it overnight, plugged in on charge, and then ran the game (the build I'd installed yesterday and which had been running at 60fps). It now runs at 20-30 fps.
I'm completely stumped. We had a similar issue on Android a while back when the newly introduced Game Launcher didn't realise our app was a game and throttled performance when the screen wasn't being touched. Is there something like that in iOS10/11? Is there a box I need to tick somewhere? Any and all help gratefully received.
