Netgear CM600 - Upstream light blinking rapidly during setup

During the initial setup for the modem, I've plugged in the coax cable and then plugged in the power source. The power light comes on solid green, then the downstream light blinks for a bit before turning solid amber, then the upstream light starts to blink. After a few blinks, the upstream light starts to blink very rapidly and never stops, even after 10 minutes.

I've tried resetting the modem, plugging and unplugging everything. There is no info anywhere about the upstream light blinking rapidly, so I'm not sure where to go next.

I have Xfinity, and I've reconnected the Xfi gateway they've provided and I'm having no issues with that. I'm also reaching out to Xfinity customer support to see if there's anything wrong from that end.

Anyone have any ideas?