I made a few changes a week ago when the connectivity was poor. I basically reset everything to zero -- no customizations, no trying to tweak performance. I did this so that, if I called Frontier tech support after the weekend, I could tell them the system was running as specified by them. I did not want anything in place that they could object to.

• On the modem, I reverted the DNS server URLs to the ISP defaults.
• On the Airport, I cleared the custom DNS server URLs (going to CloudFlare and Google Public DNS). The Airport is now using the ISP defaults.
• On the Airport, I reverted the wifi channels back to Automatic.
• I unplugged the Airport, then unplugged the modem, let them sit idle for a while, plugged in the modem, let it boot up and connect, and then plugged in the Airport. (Not sure I got the order right there, but that's what I think I did.)
• I also got a 1-foot cable to connect the modem to the DSL jack. I had a 10-foot cable before. I don't believe the length of the cable has anything to do with connection speed, but again, I wanted to remove any objections that Frontier tech support might have had to my setup. In my magical-thinking mode, the long looped cable may have picked up interference from the ancient power strip I use or maybe other cables it rubbed against. Anyway -- no problems with old, long cords.

Within a day or so, the connection stabilized. I still check Speedtest and Fast.com and the speeds are variable, but I more often see 1.5-2.5 Mbps than not. That's better than before, believe or not. Liz reports experiencing slowdowns when she works from home but the system does not fall over.

Network Logger Pro has recorded no total outages and far fewer DNS outages.

Did all my spells and incantations help? Or was it just the Frontier network going through a little crisis of faith and now it's back on its feet thanks to the love and support of its family and friends? We may never know. 

I do know that this latest round of self-reflection and meditation forced a few beneficial changes to our physical netowkr setup, and the connection is back to "good enough" (i.e., no more than two pauses, if any, while streaming Netflix to the Apple TV). 

I will continue to run Network Logger Pro for another week and Speedtest when I am suspicious.   But no more active tweaking of the system unless I encounter a real problem.