unreal 5.1.1 + metaXR 49 FFR greyed out / not working

I'm testing a project in 5.1.1 and attempting to enable FFR.

XrApi=NativeOpenXR  -  Unreal Loads, but FFR options in the Options MetaXR plugin greyed out
XrApi=OVRPluginOpenXR - Crashes unreal on startup with dx11 or dx12 rhi

Assertion failed: Size > 0 [File:D:\build\++UE5\Sync\Engine\Source\Runtime\Windows\D3D11RHI\Private\D3D11Buffer.cpp] [Line: 24] Attempt to create buffer 'FOculusXRHMD' with size 0.

UnrealEditor_D3D11RHI
UnrealEditor_OculusXRHMD!OculusXRHMD::BuildOcclusionMesh() [P:\SVR\spaceVR51_convert\Plugins\MetaXR\Source\OculusXRHMD\Private\OculusXRHMD.cpp:2711]
UnrealEditor_OculusXRHMD!TEnqueueUniqueRenderCommandType<`OculusXRHMD::FOculusXRHMD::SetupOcclusionMeshes'::`2'::SetupOcclusionMeshesCmdName,<lambda_2fad79b2e4f9b715a270c9ed185c9dc1> >::DoTask() [C:\Program Files\Epic Games\UE_5.1\Engine\Source\Runtime\RenderCore\Public\RenderingThread.h:206]
UnrealEditor_OculusXRHMD!TGraphTask<TEnqueueUniqueRenderCommandType<`OculusXRHMD::FOculusXRHMD::SetupOcclusionMeshes'::`2'::SetupOcclusionMeshesCmdName,<lambda_2fad79b2e4f9b715a270c9ed185c9dc1> > >::ExecuteTask() [C:\Program Files\Epic Games\UE_5.1\Engine\Source\Runtime\Core\Public\Async\TaskGraphInterfaces.h:1348]
UnrealEditor_Core
UnrealEditor_Core
UnrealEditor_RenderCore
UnrealEditor_RenderCore
UnrealEditor_Core
UnrealEditor_Core
kernel32
ntdll