OK

Assuming you haven’t introduced any S2 only product into your setup have you in the ordered listed….

1. Unplugged your Sonos (do not factory reset anything)
2. Deleted the Sonos app
3. Rebooted your router
4. Reboot your device (updated it if required)
5. Plugged in your Sonos and let them come back
6. Re-install the Sonos app
7. Seleted Join an existing system
8. Verified your system was found 
9. Signed in with your credentials 

I rebooted the Boost device and connected one of the Play1 devices directly with a network cable. Access to all of the other S1 devices reappeared on my app.

Glad you figured it out. However, it would have been helpful if you had included the fact that you have Boost in your system.