Internet intermittently dropping since Monday July 27

What do you mean  low to out of spec?

Upstream power levels  42.3 to  44.8

Those are both low to out of spec ! What about the upstream power level numbers ?

Not able to log into Comcast router it keeps saying incorrect user name.   This is a new router that comcast agent helped me set up. I don't know the username to use other than my comcast account username.  That is the one that gets that message.   I have tried everything else on that page except the reports.  

Ok got in.  Downstream power level ranging from -7.8 to -13.9.  Snr range from 34.7 to 37.9.     I have errors in the unerrored codewords, correctable codewords and uncorrectable codewords

The default username is admin and the default password is password

The upstream is good. The downstream is low to out of spec. That simply means that there is some sort of a connection / signal impairment to the Comcast coax cable system, so the modem is operating out of it's normal range of parameters. This will cause problems. That can cause random disconnects, spontaneous re-booting of the modem, speed, packet loss, latency problems, and the un-bonding of channels.

In a self troubleshooting effort to try to obtain better connectivity / more wiggle room, check to see if there are there any excess/unneeded coax cable splitters in the line leading to the modem that can be eliminated/re-configured. Any splitters that remain should be high quality and cable rated for 5-1002 MHz, bi-directional, and no gold colored garbage types like GE, RadioShack, RCA, Philips, Leviton, Magnavox, and Rocketfish from big box stores like Home Depot, Lowes, Target, Wal-Mart etc. Splitters should be swapped with known to be good / new ones to test

If there aren't any unneeded splitters that can be eliminated and if your coax wiring setup can't be reconfigured so that there is a single two way splitter connected directly off of the drop from the street/pole with one port feeding the modem and the other port feeding the rest of the house/equipment with additional splits as needed, and you've checked all the wiring and fittings for integrity and tightness and refresh them by taking them apart then check for and clean off any corrosion / oxidation on the center wire and put them back together again, then perhaps it's best to book a tech visit to investigate and correct.