Just as as FYI, I also use an eero system with a Gen2 Rachio controller.
My Rachio dropped offline a few weeks ago in a similar fashion. Was 'connected' when looking in the eero app, just not online from the Rachio's perspective. I assigned a static IP address to the Rachio after a hard reset of the device and the issue was resolved.
You can configure the static IP via the eero app by device if this comes up again for you.
The 'joys' of modern toys. Cheers!