Critical Modem errors: No Ranging Response received - T3 time-out

I recently upgraded my modem to an Arris S34 and have been getting a bunch of critical errors. Mostly the following:

No Ranging Response received - T3 time-out

Along with the following Notice level events:

US profile assignment change

CM-STATUS message sent. Event Type Code: 16

CM-STATUS message sent. Event Type Code: 24

DS profile config update

I chatted with support and they ran a lengthy test. They then told me to restart my modem and the problem would be solved. Unfortunately, nothing changed, and the problem continues.

I talked with Arris support, and they tell me the Upstream OFDMA channel power is too low (40.2 dBmV) to hold a good sync and is out of spec.

All the other power levels and SNRs look good, so there is probably not a problem with the modem or cables. I did replace the inside cable with a new high quality cable. There are no splitters in the path.

How do I reach a support resource that can check/adjust the upstream OFDMA channel power levels on the Xfinity side?