Gigabit Extra upload speed dropped from ~40 Mbps to ~20 Mbps after Xfinity network upgrade — severe upload latency

I have Xfinity Gigabit Extra. Before the recent Xfinity network upgrade in my area, I consistently received approximately 40 Mbps upload. Since the upgrade, my upload speed has consistently been approximately 20 Mbps, regardless of the time of day.

I recently ran Waveform's Bufferbloat test and found a significant difference between my two Internet connections:

Xfinity: approximately 559 ms upload latency under load

AT&T: approximately 63 ms upload latency under load

I have both Xfinity and AT&T Internet/Wi-Fi in my home. I ran the tests on the same computer, in the same home, using the same Waveform test. The Internet connection is the primary variable that changes between the two tests.

My Xfinity idle latency is otherwise good (approximately 41 ms), and my download speed is approximately 250 Mbps. My Zoom video calls also work normally, so I am not experiencing an obvious day-to-day service problem. However, the combination of the consistent 20 Mbps upload ceiling and the very high upload latency under load concerns me.

Because the upload speed decreased from approximately 40 Mbps to approximately 20 Mbps following the Xfinity network upgrade, and because the AT&T connection does not exhibit the same severe upload latency, I would like to have Xfinity investigate whether there is an upstream provisioning, modem configuration, or network configuration issue associated with my Gigabit Extra service.

Could an Xfinity technical representative please verify that my account and modem are correctly provisioned for the upstream service available in my area, and determine why my upload speed is now limited to approximately 20 Mbps?

I am happy to provide account-specific information through a private Xfinity Support message if necessary.