One of my sonos speaker changed ip address after I did some work on my network.
After that HE was not able to find it again.
I thought I would start on scratch so I deleted the Sonos app.
Now when I install the Sonos app again it dosent find any of my speakers... I have checked the logs and cant find anything there either.
There may be options if you can move the devices, to bring them near your non-primary
google wifi, and you may be able to set them up if you are connected to the primary router.
Once configured you can move them back (and assign them reserved IP addresses).
You can also move the device far enough away (temporarily) from the primary router such that your phone will not connect 5Ghz.