With car 2 off, reload the group then make sure all the hall calls are in the group I/O map. When you enter a DHNF command you should see all the HNs and port assignments the same as when done from the other car. They will be off line but they should be there. If that’s all there, the software should be ok. Check voltage on the CAN channel, you should have about 2.5 vdc to ground on the high and slightly less like 2.4 on the low and it should be fluctuating. Does a TECF work from car 2? If not, you probably have a problem with the teach wire. It’s a good idea to make sure all the group parameters are the same in both cars but I don’t think any of them would cause this problem. With car 1 off, record all of car 2’s group parameters, then with car 2 off, go through car 1’s group parameters and make them all the same as car 2. It’s important to do it this way or completely isolating each car from the group or you will always be looking at car 1’s group parameters.