As of iOS 18.1 being released we are having issues with our users experiencing issues with our app that relies on strobing the device torch.
We have narrowed this down to being caused on devices with adaptive true-tone flash and have submitted a radar: FB15787160.
The issue seems to be caused by ambient light levels. If run in a dark room, the torch strobes exactly as effectively as in previous iOS versions, if run in a light room, or outdoors, or near a window, the strobe will run for ~1s and then the torch will get stuck on for half a second or so (less frequently it gets stuck off) and then it will strobe again for ~1s and this behaviour repeats indefinitely.
If we go to a darker environment, and background and then foreground the app (this is required) the issue is resolved, until moving to an area with higher ambient light levels again. We have done a lot of debugging, and also discovered that turning off "Auto-Brightness" from Settings -> Accessibility -> Display & Text Size resolves the issue.
We have also viewed logs from Console.app at the time of the issue occurring and it seems to be that there are quite sporadic ambient light level readings at the time at which the issue occurs. The light readings transition from ~100 Lux to ~8000 Lux at the point that the issue starts occurring (seemingly caused by the rear sensor being affected by the torch). With "Auto-Brightness" turned off, it seems these readings stay at lower levels.
This is rendering the primary use case of our app essentially useless, would be great to get to the bottom of it! We can't even really detect it in-app as I believe using SensorKit is restricted to research applications and requires a review process with Apple before accessing?
Edit: It's worth noting this is also affecting other apps with strobe functionality in the exact same way