Issue: My android phone which does not have any SIM keeps going from the regular WiFi SSID to "Guest" SSID. If I reboot router and modem it will stay on regular SSID for a few days then it happens again; repeat, reboot, it's good for a couple of days.

I am using an old Android phone for my games only basically. It has no SSID.
One thing I want to mention is that our cable company who provides the Internet recently changed; bought out by another company.

I have made no changes on my router settings since this started to happen, no changes to my phone that does this. If I sit next to the router and modem and reboot both the phone will stay on the regular WiFi SSID, couple days later when I turn on the phone it attempts to connect to the regular SSID, keeps showing it is connecting then it says No Internet, bounces back to try and reconnect a few times and then finally settles down on the guest SSID.

I believe this started to happen when the cable companies switched over service. One good thing was that my internet speed went from 50Mbs to 100Mbs for the same price. I have had no issues with my phone that I used on a regular bases that does have a SIM and 2 other people in the house have had no problems and our TVs etc no problems.

Any ideas? A place to start maybe.

Thanks