I am seeing exactly the same behavior with UIPageViewController and ToolBarItems. The only difference is I saw it in the emulator as well, without low power mode. Did you find a workaround to prevent this from happening?

I am seeing the same crash, however my app is using SwiftUI, so I don't know how I could have added the same item to two navigation bars. Any idea what I am doing wrong? Here is my backtrace: Last Exception Backtrace: 0 CoreFoundation 0x1a2c74f20 __exceptionPreprocess + 164 (NSException.m:249) 1 libobjc.A.dylib 0x19ab7a018 objc_exception_throw + 60 (objc-exception.mm:356) 2 Foundation 0x1a217b868 -[NSAssertionHandler handleFailureInMethod:object:file:lineNumber:description:] + 188 (NSException.m:252) 3 UIKitCore 0x1a515542c -[UINavigationBar layoutSubviews] + 460 (UINavigationBar.m:3853) 4 UIKitCore 0x1a4e82a4c -[UIView(CALayerDelegate) layoutSublayersOfLayer:] + 1528 (UIView.m:20054) 5 UIKitCore 0x1a4fd9a58 -[UINavigationBar layoutSublayersOfLayer:] + 192 (UINavigationBar.m:3811) 6 QuartzCore 0x1a42e13b4 CA::Layer::layout_if_needed(CA::Transaction*) + 504 (CALayer.mm:10816) 7 UIKitCore 0x1a4ecbe90 -[UIView(Hierarchy) layoutBelowIfNeeded] + 296 (UIView.m:14159) 8 UIKitCore 0x1a4f74648 -[UINavigationController _positionNavigationBarHidden:edge:initialOffset:] + 580 (UINavigationController.m:2901) 9 UIKitCore 0x1a4fd6bd8 -[UINavigationController _positionNavigationBarHidden:edge:] + 268 (UINavigationController.m:0) 10 UIKitCore 0x1a4f7c6a8 -[UINavigationController _updateBarsForCurrentInterfaceOrientationAndForceBarLayout:] + 104 (UINavigationController.m:5388) 11 UIKitCore 0x1a512bc00 -[UIViewController viewDidMoveToWindow:shouldAppearOrDisappear:] + 164 (UIViewController.m:7062) 12 UIKitCore 0x1a5129304 -[UINavigationController viewDidMoveToWindow:shouldAppearOrDisappear:] + 76 (UINavigationController.m:4486) 13 UIKitCore 0x1a4e9b854 -[UIView(Internal) _didMoveFromWindow:toWindow:] + 1128 (UIView.m:17495) 14 UIKitCore 0x1a4e9b698 -[UIView(Internal) _didMoveFromWindow:toWindow:] + 684 (UIView.m:0) 15 UIKitCore 0x1a4e8ca70 __45-[UIView(Hierarchy) _postMovedFromSuperview:]_block_invoke + 124 (UIView.m:13611) 16 CoreAutoLayout 0x1c3df4f14 -[NSISEngine withBehaviors:performModifications:] + 84 (NSISEngine.m:1995) 17 UIKitCore 0x1a4e8f914 -[UIView _postMovedFromSuperview:] + 504 (UIView.m:13594) 18 UIKitCore 0x1a4e8e3d0 -[UIView(Internal) _addSubview:positioned:relativeTo:] + 2200 (UIView.m:18281) 19 UIKitCore 0x1a52270ec -[UITransitionView transition:fromView:toView:removeFromView:] + 868 (UITransitionView.m:368) 20 UIKitCore 0x1a5226d60 -[UITransitionView transition:toView:] + 116 (UITransitionView.m:270) 21 UIKitCore 0x1a5224c00 -[UITabBarController transitionFromViewController:toViewController:transition:shouldSetSelected:] + 2072 (UITabBarController.m:4026) 22 UIKitCore 0x1a52996ac -[UITabBarController _setSelectedViewController:performUpdates:] + 352 (UITabBarController.m:2271) 23 UIKitCore 0x1a5298948 -[UITabBarController setSelectedViewController:] + 84 (UITabBarController.m:2237) 24 UIKitCore 0x1a56cec64 -[UITabBarController _setSelectedViewControllerAndNotify:] + 428 (UITabBarController.m:3535) 25 UIKitCore 0x1a56cea94 -[UITabBarController _tabBarItemClicked:] + 48 (UITabBarController.m:3484) 26 UIKitCore 0x1a526d31c -[UIApplication sendAction:to:from:forEvent:] + 100 (UIApplication.m:5616) 27 UIKitCore 0x1a55f7d18 -[UITabBar _sendAction:withEvent:] + 384 (UITabBar.m:1525) 28 UIKitCore 0x1a526d31c -[UIApplication sendAction:to:from:forEvent:] + 100 (UIApplication.m:5616) 29 UIKitCore 0x1a526d1f4 -[UIControl sendAction:to:forEvent:] + 112 (UIControl.m:920) 30 UIKitCore 0x1a526d044 -[UIControl _sendActionsForEvents:withEvent:] + 324 (UIControl.m:991) 31 UIKitCore 0x1a55f9054 -[UITabBar _buttonUp:] + 100 (UITabBar.m:2368) 32 UIKitCore 0x1a526d31c -[UIApplication sendAction:to:from:forEvent:] + 100 (UIApplication.m:5616) 33 UIKitCore 0x1a526d1f4 -[UIControl sendAction:to:forEvent:] + 112 (UIControl.m:920) 34 UIKitCore 0x1a526d044 -[UIControl _sendActionsForEvents:withEvent:] + 324 (UIControl.m:991) 35 UIKitCore 0x1a5785894 -[UIControl touchesEnded:withEvent:] + 400 (UIControl.m:670) 36 UIKitCore 0x1a51adeac -[UIWindow _sendTouchesForEvent:] + 776 (UIWindow.m:3330) 37 UIKitCore 0x1a51ad954 -[UIWindow sendEvent:] + 3204 (UIWindow.m:3658) 38 UIKitCore 0x1a502e9e0 -[UIApplication sendEvent:] + 564 (UIApplication.m:12721) 39 UIKitCore 0x1a50301d4 __dispatchPreprocessedEventFromEventQueue + 5552 (UIEventDispatcher.m:2598) 40 UIKitCore 0x1a5038ecc __processEventQueue + 5624 (UIEventDispatcher.m:2956) 41 UIKitCore 0x1a4f2b84c updateCycleEntry + 160 (UIEventDispatcher.m:126) 42 UIKitCore 0x1a4f2976c _UIUpdateSequenceRun + 84 (_UIUpdateSequence.mm:119) 43 UIKitCore 0x1a4f293b0 schedulerStepScheduledMainSection + 172 (_UIUpdateScheduler.m:1058) 44 UIKitCore 0x1a4f2a254 runloopSourceCallback + 92 (_UIUpdateScheduler.m:1221) 45 CoreFoundation 0x1a2c47834 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ + 28 (CFRunLoop.c:1957) 46 CoreFoundation 0x1a2c477c8 __CFRunLoopDoSource0 + 176 (CFRunLoop.c:2001) 47 CoreFoundation 0x1a2c45298 __CFRunLoopDoSources0 + 244 (CFRunLoop.c:2038) 48 CoreFoundation 0x1a2c44484 __CFRunLoopRun + 828 (CFRunLoop.c:2955) 49 CoreFoundation 0x1a2c43cd8 CFRunLoopRunSpecific + 608 (CFRunLoop.c:3420) 50 GraphicsServices 0x1e7af41a8 GSEventRunModal + 164 (GSEvent.c:2196) 51 UIKitCore 0x1a527c90c -[UIApplication _run] + 888 (UIApplication.m:3713) 52 UIKitCore 0x1a53309d0 UIApplicationMain + 340 (UIApplication.m:5303) 53 SwiftUI 0x1a6e34148 closure #1 in KitRendererCommon(_:) + 168 (UIKitApp.swift:51) 54 SwiftUI 0x1a6de0714 runApp<A>(_:) + 152 (UIKitApp.swift:14) 55 SwiftUI 0x1a6dec4d0 static App.main() + 132 (App.swift:114)

Yes, this is a bug in Beta 3. There is a similar discussion in the swift forums: https://forums.swift.org/t/why-does-sending-a-sendable-value-risk-causing-data-races/73074