4K GBufferHeavyData positions written to GI Cache doesn't match what is read back later on.
This issue makes it impossible to work with 4K lightmaps unless you clear the GI Cache before every bake.

1) Create a test scene that generates a 4K lightmap.
2) Bake lighting.
3) Observe that the lightmap is ok.
4) Clear baked data.
5) Bake lighting.
6) Observe that the lightmap is broken.
7) In debug builds, this assertion is printed in the log "CacheWSData: numValidPositions should match m_OccupiedSampleCount!"