Probably your AP firewall does not allow device to device comms? Still odd to be like this. How do you set the network in your hex net without PC? In AP mode?
You can unplug all day long. You 1st must understand how the bus wiring is layed out then look who is complaining about errors against the network layout.
Get wiring diagram, look to the power train bus schematic, see which modules complains about bus, then you can guestimate about where the fault might be.