WiFi devices show "connected, no internet" (wired connection unstable too)

EDIT: changed Subject to show that the wired connection instability is no longer occasional.

I posted this in response to someone else's issue but figured I should raise my own issue here since I am not able to chat w/ an Xfinity employee due to COVID19 work from home issues at Xfinity.

My WiFi connections frequently show that my devices (phones, tables, laptops) are "connected, but no internet".  Gateway restart temporarily fixes the issue.  Online diagnostic tool tells me that something is wrong that may be impacting my internet experience and offers to restart the gateway.  This just keeps happening over and over and over again.   Preventing me from working from home, which is less than ideal during a quarantine...

Gigabit service

X86-T modem

Wireless devices are 2 Android phones, 1 Android tablet, 2 iPhones, 2 Windows 10 laptops, 1 Windows 8 laptop, 1 MacBook pro (not all online at the same time.)

Hardwiring seems to reduce, but not eliminate, the issue.

I also get an occasional "cannot assign IP address" but that is far less frequent.

I have reset the X86-T to factory defaults and had Comcast activate it.  No change.

Restarting the gateway appears to help for a time, then the issue comes back.

Any suggestions?

Matt