Environment Device: iPhone 15 Pro iOS: iOS 18.0 Framework: AVFoundation App type: Custom camera app using AVCaptureSession + AVCaptureVideoPreviewLayer I’m seeing an intermittent but frequent issue where the camera preview layer briefly flashes empty after certain interruptions, even though the capture session reports itself as running and no errors are emitted. This happens most often after: Locking and unlocking the device Switching cameras (back ↔ front) The issue is not 100% reproducible, but occurs often enough to be noticeable in normal usage. What happens The preview layer briefly flashes as empty (sometimes just a “micro-frame”) Duration: typically ~0.5–2 seconds before frames resume session.isRunning == true throughout No crash, no runtime error, no interruption end failure Focus/exposure restore correctly once frames resume Visually it looks like the preview layer loses frames temporarily, even though the session appears healthy. Repro Intermittent but frequent after: Lock → unlock device Switching camera (front/back) Timing-dependent and non-deterministic Happens multiple times per session, but not every time Key observation AVCaptureSession.isRunning == true does not guarantee that frames are actually flowing. To verify this, I added an AVCaptureVideoDataOutput temporarily: During the blank period, no sample buffers are delivered Frames resume after ~1–2s without any explicit restart Session state remains “running” the entire time What I’ve tried (did NOT fix it) Adding delays before/after startRunning() (0.1–0.5s) Calling startRunning() on different queues Restarting the session in AVCaptureSessionInterruptionEnded Verifying session.connections (all show isActive == true) Rebuilding inputs/outputs during interruption recovery Ensuring startRunning() is never called between beginConfiguration() / commitConfiguration() (Hit the expected runtime warning when attempted) None of the above removed the brief blank preview. Workaround (works visually but expensive) This visually fixes the issue, but: Energy impact jumps from Low → High in Xcode Energy Gauge AVCaptureVideoDataOutput processes 30–60 FPS continuously The gap only lasts ~1–2s, but toggling the delegate on/off cleanly is difficult Overall CPU and energy cost is not acceptable for production Additional notes CPU usage is already relatively high even without the workaround (this app is camera-heavy by nature) With the workaround enabled, energy impact becomes noticeably worse The issue feels like a timing/state desync between session state and actual frame delivery, not a UI issue Questions Is this a known behavior where AVCaptureSession.isRunning == true but frames are temporarily unavailable after interruptions? Is there a recommended way to detect actual frame flow resumption (not just session state)? Should the AVCaptureVideoPreviewLayer.connection (isActive / isEnabled) be explicitly checked or reset after interruptions? Is there a lightweight, energy-efficient way to bridge this short “no frames” gap without using AVCaptureVideoDataOutput? Is rebuilding the entire session the only reliable solution here, or is there a better pattern Apple recommends?