UPDATE: Change from Lumen to SSR resolved this issue. However, is it a Lumen limitation currently?

• Support Hardware Ray Tracing
• High Quality Translucency Reflections
• Use Hardware Ray Tracing when available
• Reflection Method: Lumen
• GI: Lumen
  
  These setting are turned on and the problem still occurs

What Ray Lighting mode are you using? Also make sure you’ve set Global Clip Plane and Custom Depth Pass Enabled with Stencil. 

Ray Lighting is set to Hit Lighting for reflections but Surface Cache gives the same result. All basic project settings are set correcly.
I'd like to mention that SSR do not have that issue but I would like to use Lumen's reflections...

Hi,

Do you have Render To Depth set to On in the Billboard panel of the camera compound?
It seems you have the other settings correctly turned on to have Lumen Reflections: https://aximmetry.com/learn/virtual-production-workflow/preparation-of-the-production-environment-phase-i/obtaining-graphics-and-virtual-assets/creating-content/creating-content-for-aximmetry-de/ue5-how-to-install-and-work-with-the-unreal-engine-based-de-edition/#lumen-reflections 

In order to achieve the best quality, the billboard is also a translucent material in the Aximmetry camera blueprint. This is why some settings can cause artifacts while the billboard is in front of other translucent materials. However, there should be no artifacts when using the settings that are in the documentation.

Warmest regards,

Hi Eifert!
I double-checked these settings and:

Hi,

It is likely caused by some custom logic in the glass material. If you can share the material, we can look at it to find out what is going wrong with it.

When Allow Virtuals is turned OFF, Aximmetry renders the image of the Billboard on top of the Unreal scene. When Allow Virtuals is turned ON, Unreal Engine renders to Billboard. That is why you only see this happening when Allow Virtuals is turned ON:
More on this here: https://aximmetry.com/learn/virtual-production-workflow/preparation-of-the-production-environment-phase-i/green-screen-production/tracked-camera-workflow/scene-control-panel/#use-billboards-&-allow-virtuals
And here: https://aximmetry.com/learn/virtual-production-workflow/preparation-of-the-production-environment-phase-i/green-screen-production/virtual-camera-workflow/setting-up-billboards-in-virtual-camera-compounds/#billboards-in-virtual-camera-compounds-with-aximmetry-de-unreal-engine-rendered 

Warmest regards,

Hi Eifert, 

I have been trying with multiple glass material setups and all of them seem to struggle the same way.
In the end I used glass material from UE starter pack - assuming it's relatively simple.

Maybe there is a specific way to how glass material should be set up when Lumen reflections are in use?

Regards,

It’s generally better to not have Allow Virtuals enabled and match the physical lights in combination with the Adjuster to match the foreground. Using lights in Unreal to light the Billboard doesn’t really work, since you’re just lighting a flat surface. 

I am aware of that, however it is good to figure this out in case Allow Virtuals is demanded.

Hi,

Hard to tell what is going wrong without seeing the material.

I don't think there is a specific way to set up glass in Lumen, however, you should use these settings: https://docs.unrealengine.com/5.1/en-US/lumen-global-illumination-and-reflections-in-unreal-engine/
Probably some reflective or translucent functionalities are still not fully supported in Lumen at certain settings, which is why you get these artifacts.

Warmest regards,

Still have not found solution for that, any ideas on how to debug this?

UPDATE: I just turned off 'Hit Lighting for Reflections" under Lumen Reflections in Post Process Volume and it seems to do the trick. However, it is a bug I guess.