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)
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.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-78112 in the post.