Hey @Yin_Yu,
There may be some confusion. In Cesium for Unreal, clipping won’t actually cut out geometry from the tiles. In other words, nothing is actually removed. Instead, it marks an area on the tileset to hide, to make transparent in the Material. It will appear to have a hole in the tile, but actually the tile’s model is still whole.
When you’re viewing the model in Wireframe, it’s going to draw all of the existing geometry regardless of the material effects on it. So yeah, it will show the entire building even though it is “clipped.” I’m not as familiar with the “Lighting Only” pass, but I imagine it is meant to show how light strikes a surface before it is applied to the material.
I hope that makes sense 