CM700 Xfinity issue

Hello, I'm running into some similar issues as the following thread with some minor differences:

https://community.netgear.com/t5/Cable-Modems-Routers/CM1000-Xfinity-issues/td-p/1445693

Problem: I should be getting 500mb download speeds from Xfinity but I'm only getting 300mb when using the Netgear CM700 modem. I have had multi techs troubleshoot over the phone and onsite. They have checked signals over the phone and onsite techs have checked the physical lines a couple of time. The last time they were onsite, they swapped out the Netgear modem with their Xfinity xFi router and we were able to get the full 500mb download speeds. We swapped it back to the Netgear modem and it went back down to 300mb. Here is a quick summary of what has been done:

- plugged Netgear modem directly to the coax cable and not through a splitter

- factory reset the Netgear modem numerous times

- speed test executed while plugged directly into Netgear modem with ethernet cable

- check the channels and did not see any "uncorrectable" counts

- checked the power and did not see anything higher than the 3.5dbmv variation between channels

I opened a ticket with Netgear a couple of weeks back and they told me the reason why I'm not getting the full download speeds was because my all upstream bonded channels needed to be "locked". They told me to get back with Xfinity and tell them to make sure all channels are locked. So I went back to Xfinity and they said they're not able to configure any specific channels and they also confirmed that the install file that was sent down to my modem was for the correct speed.

I'm stuck right now because I'm not sure if the upstream bonded channels being unlocked is the real issue. After looking through the other threads, it seems like another people shared their screenshots and their upstream bonded channels looked similar to mine. 

Does anyone have any suggestions? Could I have a faulty modem?