RAX80 not showing up in Nighthawk app when set to AP Mode

I recently bought a nice new RAX120 to act as my "main" router, which means that my RAX80 is now set to AP mode on another floor of the house, connected via ethernet to the RAX120.

The coverage is great, and I'm glad to be rid of the old router (R7000) that I was previously using as the secondary (it needed occasional reboots). However, while I can access the RAX120 through the Nighthawk Android app, I can no longer connect to the RAX80 via the Android app. I am still able to access the RAX80 from a web browser on a Windows computer, but not through the Nighthawk Android app.

Before when the RAX80 was the main and the R7000 was in AP Mode, I was able to access both routers through the Android app. Now that I have the RAX120 as the main and the RAX80 in AP Mode, I can only access the RAX120 through the Android app.

Is this by design? Is this how it's supposed to work? If not, how do I get it connected to the Android app?