I spent some really frustrated hours with the non-Pro Dream Machine before I sent it back. Instead, I‘m using a Unifi USG and two APs, and am really happy with this setup.
Not sure exactly when you had the UDM, but the earlier firmware for both the UDM and UDMP was awful and filled with bugs. It has since gotten a lot better. I haven't had any issues with my UDMP since the newer firmware and my home internet experience is much smoother than with my consumer routers (which would randomly drop connections or refuse new connections until a reboot... full NAT table maybe?)