Compacted acceleration structure size is expected to be non-zero. This error suggests that GPU readback synchronization is broken.

Development Rendering
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I really much require assistance with solving this once and for all now that I require Ray tracing to be enabled for megalights I cannot any longer have this bug as our project requires HW RT now for megalights.

AMD 6600XT up to date drivers, Unreal Engine 5.5.3

thank you

LogOutputDevice: Error: Ensure condition failed: InSizeAfterCompaction > 0 [File:D:\build++UE5\Sync\Engine\Source\Runtime\D3D12RHI\Private\D3D12RayTracing.cpp] [Line: 3456]
LogOutputDevice: Error: Compacted acceleration structure size is expected to be non-zero. This error suggests that GPU readback synchronization is broken.
LogOutputDevice: Error: Stack:
LogOutputDevice: Error: [Callstack] 0x00007ff960818f0d UnrealEditor-D3D12RHI.dll!UnknownFunction
LogOutputDevice: Error: [Callstack] 0x00007ff960722bb0 UnrealEditor-D3D12RHI.dll!UnknownFunction
LogOutputDevice: Error: [Callstack] 0x00007ff96075d095 UnrealEditor-D3D12RHI.dll!UnknownFunction
LogOutputDevice: Error: [Callstack] 0x00007ff9607730f8 UnrealEditor-D3D12RHI.dll!UnknownFunction
LogOutputDevice: Error: [Callstack] 0x00007ff9607860a1 UnrealEditor-D3D12RHI.dll!UnknownFunction
LogOutputDevice: Error: [Callstack] 0x00007ffa0c89ec3a UnrealEditor-RHI.dll!UnknownFunction
LogOutputDevice: Error: [Callstack] 0x00007ffa0c8cacb7 UnrealEditor-RHI.dll!UnknownFunction
LogOutputDevice: Error: [Callstack] 0x00007ffa0c8876d7 UnrealEditor-RHI.dll!UnknownFunction
LogOutputDevice: Error: [Callstack] 0x00007ffa0c8a02f2 UnrealEditor-RHI.dll!UnknownFunction
LogOutputDevice: Error: [Callstack] 0x00007ffa0c8a23d6 UnrealEditor-RHI.dll!UnknownFunction
LogOutputDevice: Error: [Callstack] 0x00007ff9835e2722 UnrealEditor-Core.dll!UnknownFunction
LogOutputDevice: Error: [Callstack] 0x00007ff9835d7d4a UnrealEditor-Core.dll!UnknownFunction
LogOutputDevice: Error: [Callstack] 0x00007ff9835d81ee UnrealEditor-Core.dll!UnknownFunction
LogOutputDevice: Error: [Callstack] 0x00007ff9fd2dd8a6 UnrealEditor-RenderCore.dll!UnknownFunction
LogOutputDevice: Error: [Callstack] 0x00007ff983c0c0bd UnrealEditor-Core.dll!UnknownFunction
LogOutputDevice: Error: [Callstack] 0x00007ff983c035df UnrealEditor-Core.dll!UnknownFunction
LogOutputDevice: Error: [Callstack] 0x00007ffa83cf7374 KERNEL32.DLL!UnknownFunction
LogOutputDevice: Error: [Callstack] 0x00007ffa8573cc91 ntdll.dll!UnknownFunction

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hello?

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Hey there @GreenHowitzer! Welcome back to the community!

LogOutputDevice: Error: Compacted acceleration structure size is expected to be non-zero. This error suggests that GPU readback synchronization is broken.

being the primary error makes me think that either this is an environmental issue with the GPU settings/drivers (I know you mentioned they are up to date but a clean install doesn’t ever hurt), or if this GPU has trouble with compaction as I’ve seen the 6600XT have a handful of reports on Hardware Raytracing crashing in odd ways.

Try using the command r.RayTracing.Compaction 0 which will reduce performance, but may avoid the crash.

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thank you very much I will try all of that and let you know