How to read/understand the cable diagnostics on the Nighthawk CAX80.

All that is on the modem and ISP side. They need to check it out and resolve that.

Be sure your using good quality RG6 coax cable up to the modem. 
Start with removing any amplifiers, signal attenuators, or splitters from the coax.
From there check the line for kinks, damage, moisture in the line.
Check the connectors for improperly made ends, foil touching the copper coax line, loose connections, bad/old/cheap connectors, or corroded connections. Replace them if you do.

So basically, you have validated everything I have done so far.  I had new RG6 coax cable installed in my condo less than 5 yrs ago..  As for Xfinity, they ran new cable from their box to each of the units maybe <5 years ago per my request because their service sucked so bad.  I don't have any amplifiers, attenuators or splitters from the coax.  I do have an extender installed on the Xfinity wire but get the same results with or without it.  The Xfinity tech provided me with their extender/extra coax because when Xfinity contractor ran the cables in the basement, they only ran it so far and not enough to reach any cable modem box that Xfinity or I have. Hope this makes sense.  Moving it would require the extender and more coax run from the basement to the 1st or 2nd floor.

Thank you again.