Note: I've compiled this report to address several related issues for better tracking.
Please keep in mind that I am not a native English speaker, so feel free to ask for additional details if something is unclear.

1. Occlusion by Terrain Issues:
Problem: Objects are not correctly occluded by terrain when the camera is facing specific angles.
Details: When the camera rotation falls between 135 and 315 degrees, objects are not being properly culled by the terrain, leading to performance issues.
Video Demonstration

2. Missing Occluders for Spawned Items and Occasional Occlusion Issues:
Problem 1: Manually spawned items lack occluders.
Details 1: Manually spawned objects lack occluders, while "baked-in map" (static) objects have occluders, which leads to performance issues in custom-made locations.
Problem 2: Occasionally, occluders fail to hide models that are clearly behind them.
Details 2: Certain camera angles prevent occlusion culling from functioning correctly.
Video Demonstration (both issues are captured)

3. Proxy Occluder Inconsistencies:
Problem: Proxy occluders for map objects are not working as intended. Additionally, the behavior of proxy occluders for manually spawned objects is contrary to expectations.
Details: Proxy occluders for map objects are not performing their occlusion duties as intended. The occlusion order for spawned objects is incorrect, with the main model being occluded first, followed by proxies in proxy occluders, and other proxies being occluded last, leading to performance issues.
Video Demonstration

4. Frustum Culling Disables Shadows:
Problem: Frustum culling is preventing shadows from rendering.
Details: While occlusion culling still renders shadows (even at lower resolutions), frustum culling entirely disables the rendering of models and their associated shadows. This leads to flickering shadows when within the shadow of the affected model.
Video Demonstration