Blocks that use an ambient occlusion value of 0 don't treat lighting as smooth

Issue:

Custom blocks with an ambient occlusion value of 0 render lighting as if it isn’t smooth, although a bit differently than if smooth lighting is actually disabled.

Steps to reproduce:

• Create a block (using thin geometry shows the issue better) which has an ambient occlusion value of 0

• Place it in an environment with inconsistent lighting - a small room with a single light block works best. See the attached world download for an environment setup like this. An example BP and RP are also attached.

Expected result:

The block features a smooth gradient of lighting.

Actual result:

The lighting on the block changes on each block instead of within the block. See attached image for picture of the result.

Additional notes:

Using an ambient occlusion value of 0.1 returns a very similar (though not identical) result to what 0 should look like.