For what it's worth, I was having similar issues to what some have been having in this thread. I am posting this in case it may help others with Google mesh WiFi.

I have the Google Nest WiFi with a router and one endpoint. My Touch was disconnecting from the WiFi frequently and the only workaround was to unplug the Touch and it would reconnect to the network. This went on for months and I tried a variety of solutions to no avail. At its worst the Touch was getting kicked off the WiFi many times a day, and up until this problem the Google Mesh worked perfectly for me.

I finally worked with a Google technician who ran a diagnostics test and he determined that there was one device that was stuck as a priority device. At some point I had assigned it as a priority device for an hour and it never came out of priority mode when the hour was up. This may have been causing the network to kick off the Touch as it was taking bandwidth away from a priority device. There was no way for me to see this in the Home app as it stated that I did not have any priority devices set.

The solution was to do a factory reset on the router and re-install the router and endpoint with a new network name but same password. I have been running this for a week with no issues whatsoever.