Diagnosis
The network failed to reform correctly after power was restored. The gateway eero may have booted slower than the satellites.
How to Fix It
Power down the entire system. Unplug all eeros. Start with the gateway eero. Plug it in and wait. The light will pulse blue, then go solid white. This means it has a working internet connection. Wait a full 2 minutes after it turns solid white. Now plug in your nearest satellite. Wait for it to connect and go solid white. Repeat for each satellite, one at a time, moving outward from the gateway.
If That Didn't Work
The power outage may have corrupted the gateway's software. Perform a soft reset on the gateway eero only. Press and release the reset button on the bottom once. The light will flash blue. The eero will reboot and rebuild the network. This does not erase settings.
Heads Up
For frequent outages, plug your modem and gateway eero into a good UPS (battery backup). This keeps the gateway online long enough to guide the satellites back online smoothly when power returns.