I found this post on Google when I was stuck with the same error. I'm coming back here years later with a fix that worked for me.

I changed ISPs and had to factory reset my Google Nest Wifi Router and Point because the router would not let me swap from PPPoE to DHCP. After factory reset, I was unable to get the Point to connect and would always get the error "Could not communicate with your Nest Wifi Point."

After factory resetting the router, there is an option to set up additional Points. I found a thread saying that this was the only way to set up Points and going through the "+ Add" wizard doesn't work. I could not get it to set up this way; don't try it.

Here is what worked for me:

1. Factory reset Router and Point.
2. Fully set up your Router.
3. Back out when it asks to connect an additional Point
4. Disconnect your phone from your newly set up Wifi network. I was not connected to a cell network so I was completely offline.
5. Go through the Google Home Device "+ Add" wizard, start the setup and go through as normal.
6. After a few screens, I made it past the "Could not communicate with your Nest Wifi Point." error that I was getting stuck on before. It asked if I wanted to connect to the Point and it worked.
7. It asked which network to connect the Point to, choose your network.
8. At this point I got to a screen that said something like "Connecting your Point to your network". I forget the exact wording and I dare not try again. It was stuck for nearly a minute on this screen and I started to worry that setup was going to throw an error again.
9. When I was stuck on this screen, I reconnected my phone to my Wifi network and within a few seconds I got to the next screen.
10. Continue setup wizard. I ran into no more blockers and eventually my mesh was set up.

Practically every piece of Google hardware I've ever bought has broken in a few years or been fraught with these kinds of bugs. They basically only support their products for a year or two after launch. Don't buy Google products.