Replicated objects don't behave correctly on the client-side on slopes when not sleeping. By placing two cubes on one another and slightly rotating the bottom one to create a very gentle slope, the client-side boxes start sliding around incorrectly and then jump back to the correct server position. It's worth noting that this behavior does not reproduce on static ramps, or even movable ramps that are resting and not being affected by anything.

This was reported and tested in 4.22.3 (CL-7053642). This was reproduced in 4.21.2 (CL-4753647), 4.23 (CL-7647024), and Main 4.24 (CL-7659448)

Steps to Reproduce
  1. Open the UE4 Editor and create a Blank Template project
  2. Place two cubes in the Level and set "Static Mesh Replicates" and "Simulate Physics" to True in the Actor section of the Details panel.
  3. The two cubes should be stacked on one another and the bottom one should be scaled in the X and Y directions to make the bug easier to see.
  4. Set the cubes Mobility to Movable.
  5. Under Play, set Number of Players to 2
  6. Open up Advanced Settings and set Use Single Process to False and set Editor Multiplayer Mode to Play as Listen Server under "Multiplayer Options".
  7. Start simulating the game. In the editor, tilt the lower box using the Rotation tool to produce a slope.

Results: The top client-side box will start moving uphill and then jump back to its correct position. The lower box will also slide incorrectly and jump back to its position.

Expected: The top client-side box should follow the server box's position, which is it should be completely stationary because there's enough friction to prevent the box from moving. Likewise, the lower box should just be completely stationary and not jitter.

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Won't Fix
ComponentUE - Simulation - Physics
Affects Versions4.
CreatedJul 30, 2019
ResolvedJul 19, 2022
UpdatedJul 19, 2022