I opened up the 3 failed cars. They are all now working great
Each car had a different wiring issue, but they were all wiring issues. You just have to have a lot of patience finding the issues! All three would work with the pcb and wiring stretched out but failed when I clamped them back together. I'm not 100% but possibly the wires would short or lose contact.
Thanks for the great advice, we're back to racing.