Details:
When building the XeSS plugin version 2.1.1 with UE 5.6.1, the following error occurs:

fatal error C1083: Cannot open include file: 'RHIDiagnosticBuffer.h': No such file or directory

This is triggered by the inclusion of VulkanQueue.h, which references RHIDiagnosticBuffer.h. In UE 5.6.1, this header has been moved to the RHICore module (Engine/Source/Runtime/RHICore/Public), but several plugin modules do not declare RHICore as a dependency in their .Build.cs files.

Suggested Fix:
Add "RHICore" to the PublicDependencyModuleNames in the affected modules, such as:

• XeSSVulkanRHI.Build.cs
• XeSSUnreal.Build.cs
• XeSSCore.Build.cs
• Any other module that includes VulkanQueue.h

After adding the missing dependency, the plugin compiles successfully with UE 5.6.1.

Environment:

• Unreal Engine version: 5.6.1 (source build)
• XeSS plugin version: 2.1.1
• OS: Windows 11
• Compiler: MSVC 14.38.33130 (Visual Studio 2022 Enterprise)

Thanks for your work on this plugin — it’s a great addition to UE!