Yes, I had this problem with my smart thermostat, a Sensi, which, after a neighborhood power outage, would not reconnect to my network. I have five base stations of various kinds. After a lot of HomeKit and front-panel frustration, I realized that the Sensi only connects over 2.4 GHz—this is apparently true of a lot of HomeKit devices.
So I set up a guest network on my main router, which was exactly beneath the thermostat:
- Unique 2.4 GHz network name
- Enabled access for guest network to reach rest of main network
- Connected Sensi to that network
Immediately solved the problem. This also helped me diagnose a problem with two HomeKit cameras this week as well. I have an upcoming Mac 911 article about this whole issue!