Router and cable modem are on the same UPS. I'm not certain how long the power was out but in any case the IP provider's nearby fibre node would have been out too. No backup power there. We're in a semi rural area.
Race condition....pretty sure that's what was going on.
DHCP lease length. Don't have a definitive answer there but in the past they have been pretty persistent. I'd wager the oiutage got me a new lease when things came back up though.
The outage was while we slept. Guessing my reset occurred 3-5 hours later.
No fixed DHCP address for Rachio. Do you think that would help?