Could you please check whether you have internet access on the primary modem through direct connection before trying to set up the max router? 

I am unsure of how to do that without a PC or wifi router on site. I followed the apps instructions for setting up the modem and registered it with my ISP as instructed. The S34 modem shows a solid blue light when fully booted up.

Please make sure the modem (S34) is connected to the router in the WAN port. If you are using is an android phone, go to your settings and then in the Bluetooth option please check if the ‘Surfboard Max’ is paired. Then start over the on-boarding process by reinstalling the app. 

Still won’t progress. Followed these steps. Checked internet with another router and it works. Will I have better luck with an apple phone or PC?

I'm having the exact same problem. I have a Google Pixel 5a. I've tried all the recommended steps: disabling and re-enabling Bluetooth on my phone, factory reset the router, confirmed that I have internet access when plugging in my PC directly, reinstalled the app. Still stuck on the Bluetooth connection phase.

I previously used these routers so I know they were working at one point. Is it safe to say it's a problem with the app at this point?

Please try it on an Apple phone, as you have already followed most of the steps and the Surfboard Central app is a mobile application. If the problem persists then I would suggest you visit www.arris.com/consumersupport for further assistance. 

Could you help us with your products model number?