^^ this problem. I have also emailed support about it (ticket ID 2018072522004283, currently unanswered)
The problem with debugging any netinstall problems is that, if the script does not run for some reason and therefore there is no IP address configured, you end up with a brick. There is no way to debug, you just have to guess what is wrong by trial and error. This makes development extremely difficult.
Hence asking for a serial port.
Is this 'special' version of RouterBOOT available? I am quite happy to sign an NDA and/or send you a list of over 13,000 serial numbers of routers that I have purchased from you to demonstrate that it is worth your effort to help me.