I’ve had a bunch of issues working with wheeled vehicles myself, it really needs an overhaul.
While I haven’t had your particular issue, I had an issue where my wheel colliders would be of abnormal sizes for no apparent reason, but looked fine when inspecting the PhysicsAsset. I managed to fix it by re-importing my mesh after having reset XForm on all meshes and re-rigged it from the ground up*(also deleted any traces of it from UE4)*.
Does this only happen in a MP environment? Or locally as well? If only when in MP, that is a rather peculiar issue indeed.
The warning is a bug I reported before which was supposed to be fixed in 4.15. What version are you on?