You use follow path constraint on the armature object. This is a common mistake. Do not animate the armature object, animate the bones in pose bone. So, remove the follow path constraint and add it as a bone constraint on the root widget.
Rigacar v6.0 is available for Blender 2.83
Most stuff works real flawless. Just existing parenting like parented tires to the rim seems not work and give some strange results when generating rig. I am curious if empties with the needed naming will work.
I have a lot of fun using rigacar, so I just want say thank you!
You’re right, there is an issue if reference objects (wheels, body…) are already parented when you add the rig. Empties should work fine.
I hope you will have more fun