There are a few physics related errors that pop up at runtime and at editing time that might be related:
LogPhysics:Error: Attempt to build physics data for /Game/Maps/Map.Map:PersistentLevel.MyObject_C_0.procMeshComponent.BodySetup_3 when we are unable to. This platform requires cooked packages.
LogActor:Warning: Natively added component (MyObject_C_67.DefaultSceneRoot) was left unattached from the actor’s root.
LogPhysics:Warning: PHYSX: …\PhysXExtensions\src\ExtRigidBodyExt.cpp (217) 4 : computeMassAndInertia: Dynamic actor with illegal collision shapes
LogPhysics:Warning: PHYSX: …\PhysXExtensions\src\ExtRigidBodyExt.cpp (266) 4 : PxRigidBodyExt::updateMassAndInertia: Mass and inertia computation failed, setting mass to 1 and inertia to (1,1,1)