I have been experiencing disconnect issues for my nest access points for months. They go offline and need to be rebooted several times a day. I have seen numerous posts about this over the last few months as well. When is Google going to fix this issue and do a firmware update? What's sad is I am seeing post from the new Bass pro that say the same thing.
I have a couple of things for you to check. In your advanced network settings in the Home app, do you have IPv6 enabled? If so, can you remove that and see if it changes things for you? Also, when your points go offline, do you need to perform a restart for them to come back online, or will they eventually reconnect?
Give these steps a try:
If you're using a modem/router combo, set that to bridge mode to avoid double NAT issues.
Make sure that there is minimal to no interference (concrete, bulletproof glass, metal, mirror, etc.) and the points are no more than two rooms apart.
Unplug the power from your Google Wifi devices for 2 minutes.
If the issue persists, try factory resetting your network.
Let us know how it goes.