Internet speeds decreased drastically after upgrade from 1200Mbps plan to GIG X2 plan

Hi,

I upgraded from the 1200Mbps plan about 2 weeks ago. I used to get ~1250Mbps every time I used to run a speed test. I upgraded to the GIG X2 plan hoping to take advantage of the faster download and upload speeds. But my download speeds have been cut in half (600Mbps now) and upload went down from 50 to 60 Mbps down to 8 Mbps. 

I had a tech come in and take a look and the tech is able to do 2100Mbps down and 400Mbps on the wire directly. But he is not able to get anything more than 600 to 700 down and 10 up using my modem. I showed him my network is capable of Multi Gig by transferring a large file locally hitting more than 1Gbps. So the issue is definitely not on my local network.

My Hardware

Modem: Netgear CM2050V

Router: ASUS AXE16000 with 10G and 2.5G ports

The tech tells me that there is a known issue and Xfinity is unable to provide 2Gbps speeds and they are still working on it. But he could not explain why my speed got cut. I am expecting I should be able to get atleast as much speed as I was getting from before. He recommended that I downgrade my service back to the 1200Mbps plan. I am not entirely convinced that this is the right answer. Especially considering the raw wire is able to do 2000Mbps+ down and 400Mbps up. 

Is there anything wrong with my modem or some firmware that Xfinity is pushing to the modem? My modem is on the Xfinity approved list and is Docsis 3.1 compatible. Seems like this has happened to others on Xfinity provided modems (XB8). Here is an example thread ‎Much slower speeds after upgrade to 2GB plan and XB8 | Xfinity Community Forum

Can somebody help me figure out what is going on? The call center support people and in person techs are not able to help with it.

Thanks!