Frequent Loss of WiFi Connectivity

I frequently lose WiFi connectivity within my home.  I'm careful to say "WiFi" and not "Internet".  As I work from home, having a constant internet connection is crucial.  My internet router/modem (Model XB7) is in the same room as my home office.  Since they are in the same room, I've hard wired my home computer to the router/modem via an ethernet cable.   Whenever I lose connectivity, my home PC still has an internet connection because it's hard wired.  However, everything that's on WiFi (TV's, smart devices, etc.) loses connectivity.  Sometimes this is only for a minute or two, and other times it's slightly longer.  This happens frequently throughout the day and becomes very frustrating.  Every couple of days I will restart the router/modem to see if this helps, but it really doesn't.  My home has 3 floors.  The router/modem is on the middle floor, and there is an xFinity WiFi extender on the 1st (game room) and 3rd (bedrooms) floor. 

Another strange thing that I've observed is that this seems to happen most often whenever someone leaves or arrives at the house.  Although I can't explain why.  I'm wondering if possibly the addition/removal of a wireless device has the WiFi briefly redistributing load between the router/modem and extenders.  But that's just a guess.

I'm really hoping that there are logs being kept somewhere on the router/modem that shows this same thing occurring and someone could review those logs to point to a specific issue.