IOS 9+ Performance

I wonder if you could help me: I have an app that runs really smoothly on IOS8.4 but on every version from 9 up to 10.3.2 the scrolling / animation is terrible. The framerate seems to randomly drop from 60 to 30fps every second making it very choppy indeed, even when drawing almost no sprites at all.

I have tried an iPhone 6/7 and iPad

Anyone else have this problem?

I have the same issue on Android and started a topic. Link.
Every second the framerate drops briefly. Nobody could really help me.
In the meantime I suspect that the SDL-ACTIVITY itself is the reason.I also have learned that in the SDL-Activity SDL itself only runs in a side thread, not in the main thread. Maybe that is the problem.