It's unclear to me if these issues are happening when you are running the iOS app on your Mac (emulating during development)? If so, try setting Mac to use the

It's unclear to me if these issues are happening when you are running the iOS app on your Mac (emulating during development)? If so, try setting Mac to use the discrete GPU all the time and see if it keeps happening. MacOS flip/flopping between discrete and integrated GPU was an issue for me. I can only imagine what MacOS might be doing during development of a graphics app such as yours.