Hello mrlentini,
Firstly, I want to thank you for the extensive additional testing and feedback that you have done with rs.local/ and its behavior on Mac.
I will pass everything on to our team, and I’m sure this will definitely be of help for them.
To address your current issue, I would say that the fastest way to access the Shake OS interface in your situation would be writing down the IP address of the Shake that the admin panel of your modem/router or that the Fing app (more info here: Please read before posting!) is providing you, and using that in your browser instead of rs.local/. In these conditions, the IP address becomes a valid alternative.
That should give you access to the Shake panel, and you should be able to proceed from there.