I got a similar _dispatch_assert_queue_fail crash but the stack trace looks a bit different. I couldn't find the root cause since the stack trace does not show anything related to our code. Do you have any idea? Interestingly, this crash happens only in iOS 18+. Note: I attached the full stack crash.txt trace -[UIImageView _mainQ_beginLoadingIfApplicable] _dispatch_assert_queue_fail Crashed: com.apple.SwiftUI.AsyncRenderer EXC_BREAKPOINT 0x000000019c21e3b4 Crashed: com.apple.SwiftUI.AsyncRenderer 0 libdispatch.dylib 0x63b4 _dispatch_assert_queue_fail + 120 1 libdispatch.dylib 0x633c _dispatch_assert_queue_fail + 194 2 UIKitCore 0xb80c4 -[UIImageView _mainQ_beginLoadingIfApplicable] + 76 3 UIKitCore 0xb7fb4 -[UIImageView setHidden:] + 68 4 UIKitCore 0xb7d70 -[UIButtonLegacyVisualProvider _updateImageView] + 372 5 UIKitCore 0xe8830 -[UIButtonLegacyVisualProvider baselineOffsetsAtSize:] + 196 6 UIKitCore 0xe8748 -[UIButton _baselineOffsetsAtSize:] + 52 7 SwiftUI 0x29a48 PlatformViewLayoutEngine.explicitAlignment(_:at:) + 124 8 SwiftUI 0x299c0 protocol witness for LayoutEngine.explicitAlignment(_:at:) in conformance PlatformViewLayoutEngine<A> + 16 9 SwiftUICore 0x136f4 LayoutEngineBox.explicitAlignment(_:at:) + 120 10 SwiftUICore 0x135a4 LayoutProxy.explicitAlignment(_:at:) + 244 11 SwiftUICore 0x129d4 UnaryLayoutEngine.explicitAlignment(_:at:) + 208 12 SwiftUICore 0x13718 protocol witness for LayoutEngine.explicitAlignment(_:at:) in conformance UnaryLayoutEngine<A> + 16 13 SwiftUICore 0x136f4 LayoutEngineBox.explicitAlignment(_:at:) + 120 14 SwiftUICore 0x12130 StackLayout.UnmanagedImplementation.explicitAlignment(_:at:) + 348 15 SwiftUICore 0x307b8 StackLayout.explicitAlignment(_:in:proposal:) + 136 ... 57 SwiftUICore 0x1b5000 ViewGraph.updateOutputsAsync(at:) + 560 58 SwiftUICore 0x1b45d4 ViewRendererHost.renderAsync(interval:targetTimestamp:) + 524 59 SwiftUI 0x69d40 UIHostingViewBase.displayLinkTimer(timestamp:targetTimestamp:isAsyncThread:) + 256 60 SwiftUI 0x691d8 DisplayLink.displayLinkTimer(_:) + 280 61 SwiftUI 0x69094 @objc DisplayLink.displayLinkTimer(_:) + 60 62 QuartzCore 0xec1a4 CA::Display::DisplayLinkItem::dispatch_(CA::SignPost::Interval<(CA::SignPost::CAEventCode)835322056>&) + 48 63 QuartzCore 0xebb78 CA::Display::DisplayLink::dispatch_items(unsigned long long, unsigned long long, unsigned long long) + 884 64 QuartzCore 0xc3b58 display_timer_callback(__CFMachPort*, void*, long, void*) + 456 65 CoreFoundation 0x79b68 __CFMachPortPerform + 176 66 CoreFoundation 0x79aa4 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION__ + 60 67 CoreFoundation 0x799c4 __CFRunLoopDoSource1 + 524 68 CoreFoundation 0x762ac __CFRunLoopRun + 2248 69 CoreFoundation 0xc8274 CFRunLoopRunSpecific + 588 70 Foundation 0x29b48 -[NSRunLoop(NSRunLoop) runMode:beforeDate:] + 212 71 Foundation 0x25d10 -[NSRunLoop(NSRunLoop) run] + 64 72 SwiftUI 0x375f60 specialized static DisplayLink.asyncThread(arg:) + 792 73 SwiftUI 0x375c30 @objc static DisplayLink.asyncThread(arg:) + 72 74 Foundation 0x115a54 __NSThread__start__ + 724 75 libsystem_pthread.dylib 0x17d0 _pthread_start + 136 76 libsystem_pthread.dylib 0x1480 thread_start + 8

I'd like to make my question more clear I know adding receive(on: DispatchQueue.main) or subscribe(on: DispatchQueue.main would fix this. I know $0 which is the @Published is accessed in background (map function in this case). What I don't understand are: Why the map run on background, not on main? Why there is discrepancy in iOS 18 and iOS 17 and below. And interestingly, I observe that the map function run on background only the first time, perhaps the subscription is done in background?