Google is having some sort of issues with accounts today, and apparently that caused[0] a lot of their mesh routers to reset to factory defaults. Not sure how widespread this is, but there are a TON of people who are not happy.[1]
For my part, I reconfigured my routers this evening, and then a few hours later, they reset themselves again.
The beauty of cloud-managed hardware...
[0] https://support.google.com/wifi/answer/7335595
[1] https://productforums.google.com/forum/m/#!category-topic/googlewifi/Wifi/38Q-v9lBDRg