Modem not syncing to DOCSIS 3.1 level (no blue light)

In a post here (https://forums.xfinity.com/conversations/your-home-network/docis-31-issues/604cc285c5375f08cdbb4c5b) the poster said that his modem wasn't syncing to DOCSIS 3.1 levels as evidenced by the blue LED not being lit. I seem to be having the same issue.

The modem is an Arris SB8200. The downstream levels look OK with most channels SNR in the low 40's except for 159 which is at 26.5 at the moment. The upstream looks a little hot which channel 1 at 49.0 and the other four at 50 db.

I had thought that I needed to replace the modem but after reading the other thread I decided I would post here for advice first.

Thanks for reading!

Bill W