UE 5.1 3D Tileset collisions with physics simulated actors not working correctly

Hello everyone,

I’m seeing actors with physics simulation enabled penetrating or falling through a Cesium 3D Tileset surface in UE 5.1, but it seems to work fine in 5.0.3 and 4.27. I’m using the official Cesium for Unreal Engine Samples 03_CesiumDenver map.

This happens by placing some actors with “Simulate Physics” enabled in the map and going into play mode. I’m only considering the cases where the camera is looking directly at the tiles where the collision should occur. It still happens if I pause the tileset updates and no camera or character movement is involved (See attached videos). I’ve also tested this with the World Terrain + Bing imagery and other tilesets and the result is pretty much the same.

I know there are some expected jiggles or jumps in physics simulated actors when the tile LODs are being switched. I also know that when a tile goes out of frustum it is unloaded and thus its collision mesh is also unloaded, so I’m not considering those cases.

Apparently the third person character is colliding correctly with the tileset, as I can move it around without issues.

Unreal Engine version

Cesium for Unreal version

Steps to reproduce

  1. Open Cesium for Unreal Samples map “03_CesiumDenver”
  2. Add some basic Cubes in front of the Player Start point, just ensure to place them high enough in the air to give Unreal time to load the tileset before the Cubes fall to the ground
  3. Enable Simulate Physics on the added cubes. (Enable Gravity should already be enabled by default).
  4. Go into play mode
  5. Do not move the camera to avoid the tiles from unloading


  1. UE 5.1 (Link to video)


  1. UE 5.0.3 (Expected behavior. Link to video)


Do you know if I’m missing something? Perhaps after the upgrade to 5.1 additional setup is required? Or maybe this is a bug?

Any help is appreciated, thanks!

1 Like

Hi @leor,

You’ve already checked most of the things I would suggest. The only additional thing I can think of is to look at some of the collision related debug views and see if anything looks off in 5.1, which would probably indicate Cesium is somehow building the physics meshes incorrectly. If the collision meshes look correct but still collision isn’t working properly, it’s hard to see what Cesium might be doing wrong. At that point I’d suggest looking at the UE 5.1 release notes for anything that changed in the physics engine (there’s a long list!) and perhaps raising the issue with Epic to see if they have any ideas.


I am also struggling with the same issue!

Same issue. It’s 5.1 specific.

Any progress on this? We upgraded an entire project from 5.0 to 5.1 and only discovered just now that any object with physics simulated now falls through the terrain.

Following up – this issue is fixed in 5.2 preview.

Hi @aMahvan,
How were you able to access version 5.2 of the cesium plugin? I thought it only supports up to 5.1.

I didn’t. I forced 5.1 to work inside of UE 5.2