LittleTiles blocks do not recognize the collision correctly.

The problem comes from Radium
Reforged-Hub/radium-upstream#26

Unfortunately I don't see a way to fix it on my end. I do some optimisations for the collision, because minecraft cannot handle the amount of boxes my blocks have. Seems like Radium does something quite similar.

In the Radium settings (lithium.properties)
mixin.shapes.specialized_shapes = false
To fix the collisions, not sure if this breaks anything else though

@MichelJonkman thanks for your hint. I will close the issue for now as it cannot be fixed unfortunately.