I had same issue for quite some time and just found that decreasing “Min Contact Offset” 10 times almost fixes issue. Resulting in acceptable behavior in my case (just a little bump sometimes).
Go to Project Settings > Engine > Physics > Simulation an decrease variable “Min Contact Offset” from 2.0 to 0.2. But beware that changing physics settings might result in undesired unstable behavior, so make sure to backup settings (just screenshot it) before modifying as there is no option to reset to defaults.
Also additional step would be to modify sliding cube collision mesh to more smoother. Beveled edges should do the trick. Same can be done with level ground mesh, but but keep in mind that there will be gaps between meshes.