This, to me, is just INDI configuration and not nStep related.
I assume all devices use the underlying INDI port/device selector when dealing with 'serial' interfaces.
I have the same issue on a PI for the Celestron Nexstar device selection.. If I have the Celestron connected at power on or not previously connected after power on I see a
If I unplug/replug the Celestron I then see it enumerate on /dev/usbmodem1 (a different /dev entry)