why of 2 identical micro-controllers, only one can connect to a given device?
Other than a software issue, there is no reason it shouldn't work. Only thing may be identical Bluetooth names or ids. Clear the device from windows and try again. 

I have some cheap Bluetooth obd 2 readers that all use the same Bluetooth mac address and name. I have to delete one from my android phone before adding the new one to connect to it.