[AVCaptureSession startRunning] from background crash seldomly

The crash stack as following
Thread 0#0 (null) in CFEqual ()
#1 (null) in CFCachedStringEqual ()
#2 (null) in CFCachedStringEqual ()
#3 (null) in _CFXNotificationRegistrarFindName ()
#4 (null) in CFXNotificationRegistrarFind ()
#5 (null) in _CFXNotificationPost ()
#6 (null) in -[NSNotificationCenter postNotificationName:object:userInfo:] ()
#7 (null) in -[UIScreen _postBrightnessDidChangeNotificationIfAppropriate] ()
#8 (null) in _UIScreenBacklightLevelDidChangeCallback ()
#9 (null) in __CFNOTIFICATIONCENTER_IS_CALLING_OUT_TO_AN_OBSERVER__ ()
#10 (null) in ___CFXRegistrationPost_block_invoke ()
#11 (null) in _dispatch_call_block_and_release ()
#12 (null) in _dispatch_client_callout ()
#13 (null) in _dispatch_main_queue_callback_4CF ()
#14 (null) in __CFRUNLOOP_IS_SERVICING_THE_MAIN_DISPATCH_QUEUE__ ()
#15 (null) in __CFRunLoopRun ()
#16 (null) in CFRunLoopRunSpecific ()
#17 (null) in GSEventRunModal ()
#18 (null) in -[UIApplication _run] ()
#19 (null) in UIApplicationMain ()
#20 0x0000000102c88fa4 in main at AppDelegate.swift:19
#21 (null) in start ()
Thread 1
Thread 2
Thread 3
Thread 4
Thread 5
Thread 6
Thread 7
Thread 8
Thread 9
Thread 10
Thread 11
Thread 12
Thread 13
Thread 14
Thread 15
Thread 16
Thread 17
#0 (null) in mach_msg_trap ()
#1 (null) in mach_msg ()
#2 (null) in __CFRunLoopServiceMachPort ()
#3 (null) in __CFRunLoopRun ()
#4 (null) in CFRunLoopRunSpecific ()
#5 (null) in -[AVRunLoopCondition _waitInMode:untilDate:] ()
#6 (null) in -[AVCaptureSession _buildAndRunGraph] ()
#7 (null) in -[AVCaptureSession _setRunning:] ()
#8 0x00000001042ff4cc in __27-[CameraKit startCapture]_block_invoke at CameraKit
#9 (null) in _dispatch_call_block_and_release ()
#10 (null) in _dispatch_client_callout ()
#11 (null) in _dispatch_lane_serial_drain ()
#12 (null) in _dispatch_lane_invoke ()
#13 (null) in _dispatch_workloop_worker_thread ()
#14 (null) in _pthread_wqthread ()
#15 (null) in start_wqthread ()
Thread 18
Thread 19
#0 (null) in OUTLINED_FUNCTION_3 ()
#1 (null) in dispatch_source_cancel.cold.1 ()
#2 (null) in __FigRPCDisposeServerConnection_block_invoke ()
#3 (null) in _dispatch_client_callout ()
#4 (null) in _dispatch_lane_barrier_sync_invoke_and_complete ()
#5 (null) in FigRPCDisposeServerConnection ()
#6 (null) in RemoteQueueClientFinalize ()
#7 (null) in FigBaseObjectFinalize ()
#8 (null) in _CFRelease ()
#9 (null) in rqReceiverFinalize ()
#10 (null) in _CFRelease ()
#11 (null) in __rqReceiverSetSource_block_invoke_2 ()
#12 (null) in _dispatch_call_block_and_release ()
#13 (null) in _dispatch_client_callout ()
#14 (null) in _dispatch_continuation_pop ()
#15 (null) in _dispatch_source_invoke ()
#16 (null) in _dispatch_lane_serial_drain ()
#17 (null) in _dispatch_lane_invoke ()
#18 (null) in _dispatch_workloop_worker_thread ()
#19 (null) in _pthread_wqthread ()
#20 (null) in start_wqthread ()
Thread 20
Thread 21
Thread 22
Thread 23
Thread 24
Thread 25
Thread 26