Download speed limited to 300 Mbps on 1.2gig plan . Throttling ?

I have been working on setting up a standalone pfSense router, with my XB7 in bridge mode. I check the speed frequently with Ookla speedtest, native windows app.

My LAN is 10 GBASE-T.

I normally get a little over 1400 Mbps download speed.

However, recently, speed has been dropping to 300 Mbps in the middle of the day. I can't really explain why. There is no associated configuration change that I made.

I did a factory reset, and multiple power off/on of the XB7 gateway, but it did not fix the issue. My (wired) speed remains limited to 300 Mbps. This shows up not just in Speedtest but in Steam game downloads as well, which could previously max the 1400 Mbps (150-175MBytes/s DL speed).

Is this coming down to busy times of day for Comcast ? Or is Comcast detecting that I'm not using their router somehow, and limiting my speed down ?

FYI, to rule out my pfSense box, I see the same max 300 Mbps speed even if I revert the gateway from bridge mode back to router mode, and connect to the gateway directly.

This is very puzzling to me. Is there any workaround/solution to avoid getting throttld ?