ios - AVCaptureSession bug persists between installs -

i have app opens straight camera based on wwdc sample: https://developer.apple.com/library/ios/samplecode/avcam/introduction/intro.html

a few users have been experiencing bug camera not turn on , not allow them capture content.

i ran same issue last night , observed:

1. i debugging separate issue , camera working 100% ok, of sudden, stopped working.

2. every time open app or navigate camera, show dark view of whatever pointing at, image frozen. worked 1 second, capture preview freeze.

3. i tried force closing , reopening, same problem.

4. i tried uninstalling , reinstalling, same problem.

5. i restarted phone , issue solved.

how possible bug persists between separate installs?

does know might causing camera fail?

how should go debugging if occurred once after months of using , have no idea triggers it?

are running ios 9? might ios 9 software internal bug. had same non-reproducible issues mapkit's map view rendering. in case map view showing rectangle grid without map objects - no streets, lakes, rivers, etc.

i've tried google on internet find potential reason of such weird issue, without luck. i've restarted device , helped, same in case.

sure, info not full answer, want share experience.