In the directional light, just above “Force Cached Shadows…”, there’s the setting “Dynamic Indirect Lighting”. Disable it, as it’s for injecting light into the Light Propagation Volume. The light propagation volume has to be enabled in the config file it’s in, outside of the application, so unless you have a massive scale LPV…it’s not necessary to enable that setting.
The one thing I noticed is the flickering / flashing (noise) occurs within a certain range of the camera, and close to the camera. The CSM settings have a distance coverage of 20,000, and the video shows flickering within that distance from the camera. Try increasing the distance for CSM cascades to 100,000, and see if it results in flickering further from the camera. That’d be one way to isolate that as the cause, or a part of the cause. Another thing is LOD levels. If there’s no LODs for the grass, then it’s using the highest resolution MipMap for all of it, which could be an extreme load on the available memory and processing for that aspect of the scene. I don’t know if it would cause flickering, but it’s possible if memory is running out.
Is there a Post Process Volume that is Unbound?