Bob recently bought an eero mesh router. It worked fine for two weeks and then he started experiencing dropouts, and he can't get support. Leo says that support is terrible these days because of limitations due to CoVid. Another thing to look at is your ISP and cable modem. Security software could also be an issue and can inhibit your internet access.
Also, try and reboot the main gateway by unplugging, waiting a few minutes and then plugging back in. If that fixes it, it's likely a hardware issue. Take out the old gateway and use the new one. See what happens. Here's how. Contact eero and request a replacement.