Virtual Shadow Maps on Spot Lights cause a blocky presentation similar to an incorrect mip level

Spot Lights may present with very blocky shadow artefacts when a long attentuation radius is provided with a small cone angle. In extreme cases, this causes the VSMs to invalidate every frame. Notably, enabling the visualisation viewmodes for VSMs typically resolves the issue. If the issue does not resolve with a view mode such as clipmap, then the invalidation condition has likely been met and can be confirmed by checking the cache view mode.

Shortening the attentuation radius or increasing the cone angle does resolve the issue, but the issue may occur on values such as 2536 by narrowing the cone further. Other lighting types, such as RectLights, do not exhibit this issue. Setting a rect light to 16384 with a very small size still provides non-blocky shadows.

• Create a spot light in a level with no other lights
• Give the spotlight a 16384 attentuation radius (Can be lower. Values of around ~4000 will cause this depending on the cone angle. It seems dependent on the ratio of cone angle to attentuation radius).
• Set the cone to 5°.
• Place the light far away and point it at a sphere.

Expected: Normal VSM-type shadows from the sphere
Actual: Blocky shadows akin to very low resolution shadows.