I got bitten by this last night. Luckily it was a mesh Wifi point that lost its mind, so I just removed it and re-added it.
If it had been the primary Wifi point I would have had to reconfigure everything (SSID, password, fixed IP addresses). At least according to
https://support.google.com/wifi/answer/7335595
PS - I don't think it was an update that did this, it was something they broke in the Google Accounts engine. From an email I got yesterday:
Dear Google Wifi & OnHub customers,
Today we experienced an issue with our Google Accounts engine that may have affected your Google Wifi and OnHub devices. This caused some devices to automatically reset to the initial state you bought them in and they will unfortunately need to be set up again. This has not affected the software or performance of the device but it does need to be re-setup...