X-class upload speed capped at 120mb

It was self-install. Tech support via app chat re-provisioned my gateway, but it didn't help.

@user_3shbtt thanks for confirming, I'd like to do everything I can to help, please send a direct message including your full name and service address, and we can get started anytime.

How to Send Us a Direct Message:

1. Click "Sign In" if necessary.
2. Click the "Direct Messaging" icon or visit Xfinity Direct Messaging.
3. Click the "New message" (pencil and paper) icon.
4. In the "To:" line, type "Xfinity Support".
5. As you type, a drop-down list will appear. Select "Xfinity Support" from that list.
6. An "Xfinity Support" graphic will replace the "To:" line.
7. Type your message in the text area near the bottom of the window.
8. Press Enter to send it.

Thanks to Xfinity support on this forum for a speedy resolution. It turns out that the culprit was selecting "use my own equipment" when signing up for the 1000/1000 plan. I naively thought the CODA would work for such speeds (as the official supported modem list on Xfinity implies). Actually XB10 is the only thing compatible with X-classs / FDX speeds. By choosing "use my own equipment", my plan was silently coded as 1000/100, and even connecting an XB10 won't bring it back to the faster speed. I think Xfinity can definitely improve the ordering process with respect to using ones own modem. It is understandable that speeds are dependent on the equipment; but downgrading the plan itself is not the right way.