I did recreate same scenerio in unreal engine 5.4.4-
Created Class Inheriting from WheeledVehiclePawn and then another Class (Child BP) Inheriting it.
It wasn’t Simulating Physics until Simulate Physic was Checked in Child BP. After that Physics was working Fine
So as I mentioned in my previous response, it might be because of Properties Override changing because of Reparenting, Have you confirmed that all Properties are Correct (Especially Simulate Physics)? If So then other Possibility might be because of Physics Asset (Since it is responsible for Skeletal Mesh Collision and Physics Simulation)
I would recommend Double Checking Steps in this Video-
