Why is new Motorola MB8611 is providing lower upload than the old MB8600?

I'm on the 1.2G plan and to get the full benefits I updated my modem from Motorola MB8600 to MB8611. My Ubiqity UDM-Pro doesn't allow for LAG, but for up to 10G on the WAN ports. 

Now, the MB8611 is showing the 2.5G link to the UDM-PRO and the Internet connection is established. Download ~714Mbps but upload is only ~5Mbps. With the old MB8600 it's ~960Mbps down and ~40Mbs up. For testing I also tried the Arris S33 with pretty much the same slow speed as the MB8611, and I also tried the different LAN ports in the Arris (1G & 2.5G) with the same results.  

The error logs for all (3) modems are pretty much identical and show channel 25 as OFDM-PLC and all other channels as QAM256, and all modems show (4) upload channels. 

Speed test with Okala Speedtest against the same Xfinity Server 8miles away. 

And of course IPv4 vs v6, or different SFP+ 10G modules makes no difference. 

What to do next?