@TP-Link  I am having a similar issue to those mentioned and have tried all of the fixes recommended here.  Summarizing the issue below:

Current Setup and attempted fixes:

Have the Deco X20's set up as the following:

• (1) plugged in to the Fios Gateway Router with an ethernet cable acting as the main router for the house.  I disabled the wifi on the Verizon Router.  
• (1) Located in my family room roughly 35 feet from the router location connected via Wifi, shows full strength connection. 
• (1) Located in the upstairs gym roughly 35 feet from the router location connected via Wifi, shows full strength connection. 

I have updated and confirmed the latest firmware on each device. 

I have completely abandoned the system and reset everything to try again. 

I have power cycled each device in multiple different iterations when the problem occurs. 

I have Verizon Fios 1GB internet.  

I have roughly (30) lightbulbs connected, (5) amazon alexas, Ring system, Sonos system, (2) Desktops, (2) Laptops, (4) TV's all connected to the network.  But the issue only occurs when the below happens.  

The general issue:

Everything works just perfect, full coverage throughout the home good speeds (300-600mbps) no issues with dropped devices or "blips".  This is until both my wife and I start using our computers and laptops for work in the morning.  We both have new laptops and desktops that have no general issues if only one of us is using the wifi network at a time.  

What happens is that I get on my computer, everything is working fine all (2) hubs are green and the router has a stable connection.  My wife logs on and starts working and the problems occur.  The (2) hubs go flashing red and drop internet connection, sometimes the main router drops connection but only if the 2 hubs remain plugged in.  As soon as I unplug the (2) hubs the main router functions fine after a power cycle and doesn't drop a connection with everything working in the home (this is not ideal as its not a full strength connection for everything).   The (2) hubs after a power cycle will go green for 1-5 minutes then the problems just start over again.  

Current Workaround:

The only way I can get everything to function in the house is to unplug the (2) hubs, making them worthless and just deal with the less than ideal coverage of the single router unit.  

Would really appreciate any help I can get as this is very tough with both of us working from home.  Im tempted to return everything but I would really prefer not to have to set up a brand new wifi network again and connect all of the devices.  Please let me know if there are any suggestions!