Upload speed dropped from ~350 Mbps to ~100 Mbps after plan "upgrade"

I recently "upgraded" my Xfinity plan, but my upload speed dropped from approximately 350 Mbps to 100 Mbps afterward.

I am using the exact same modem, router, coax wiring, Ethernet setup, and client equipment as before. Nothing changed on my side.

I am using my own DOCSIS 3.1 modem, and I understand that it cannot support the full symmetric 1 Gbps upload speed of the new plan. I am not expecting 1 Gbps upstream from this modem.

What I am trying to understand is why the same DOCSIS 3.1 modem was previously delivering around 350 Mbps upstream, but after the plan change is now limited to roughly 100 Mbps upstream.

My modem is still locking normally and shows:

• 4 SC-QAM upstream channels
• 1 OFDMA upstream channel
• OFDMA channel ID 43, 44.4 MHz wide
• Upstream power around 43.5–46.8 dBmV

This looks like a provisioning/profile issue rather than a signal or equipment problem. Could an Xfinity employee please restore the same provisioning/profile that was previously applied to this modem and was delivering approximately 350 Mbps upstream? The modem, wiring, and local network setup have not changed, so I would like the previous DOCSIS 3.1 upstream profile restored if possible.

I can provide my account information, modem MAC address, before/after speed tests, and full channel statistics privately by DM.