"This Site Cannot Be Reached" Intermittent Issue

I tried the DNS flush as well as rebooting the gateway (which I had tried several times previously) and those didn't help.  Let me explain my issue a little more.  I'm using WiFi on my laptop.

Imagine I'm streaming a movie on my TV on Peacock and downloading an audiobook from the library on my laptop using the Overdrive app.  I open a browser and try to go to Facebook or Yahoo Mail, where I had successfully gone 5-10 minutes prior and I now get the "This site cannot be reached" msg.  Meanwhile my streaming movie continues and the audiobook download continues without a problem.  For 1, 5, sometimes 10 minutes no matter what site I try, I get the "This site..." msg.  Then all will go back to working for an hour or two.

During this time, my land phone plugged into the back of the gateway works.  However, I have very bad cell reception and use wifi calling for my cell which works well - except it stops during these "This site..." periods.  Meanwhile, my wife sitting across the table is having the same issues with her notebook (on Wifi) and a neighbor 4 doors down says he has similar issues.  Yesterday I dug out an older laptop with a network card and plugged it into the gateway with an RJ45 cable.  I've yet though to get to it during an outage to see if hard-wired works.  That's where I stand today.  Thoughts?