CSM Cached Shadows missing when changing FOV

When changing the camera FOV with r.Shadows.CSMCaching enabled, the cached shadows don't appear to be used and shadows are missing. This occurs because the r.Shadow.RadiusThreshold can be low enough to exclude some objects from CSM, but they are included in the cached shadows, this is particularly noticable on the Medium scalability setting and below where r.ShadowRadiusThreshold is higher and the internal screen resolution often is lower.

Update: This issue may be specific to non-Nanite ISMs which are culled on the GPU and which can use IsInstanceVisible in BuildInstanceDrawCommands.usf which calls Cull.ScreenSize(DrawCommandDesc.MinScreenSize, DrawCommandDesc.MaxScreenSize);

Steps to Reproduce

1. Set scalability to Medium so r.Shadow.RadiusThresdhold is 0.05
2. Press Play and right click to animate fov in sample project
3. Observe shadows culling when they shouldn't