He could be running in a “Playground” not an “App” which means he has to set PlaygroundPage.current.needsIndefiniteExecution = true. This gets everyone starting out.

To makes things clearer: when the issue was triggered some of the intensive CPU work was assigned to efficiency cores and remained bound to those cores until computation settled down even if computation meant multiple awaits with many small short lived workloads. That is, when things became completely idle for long enough (fraction of a second?) only then the binding of one or more of the actor threads to the efficiency cores ceased and normal performance resumed for future computation.

Limiting how many hard working threads withTaskGroup creates to the number of total cores minus 1 could be what worked to fix this - I haven’t experienced the issue since then.

I have more than 8 lights in my scene (13, but I need more). About 2-3 per SCNNode with categoryBitMask for each group of 3, so no more than 3 are illuminating a specific SCNNode. I have even added the lights as children of the illuminated SCNNode so they’re not all in the same SCNNode. Yet only 8 lights are enabled by SceneKit at a time. Any way around this? I was going for some much needed lights fine tuning which is now impossible.