The problem

I was experiencing significant ping spikes after installing a Deco X20 router with 3 nodes. When calling people or playing games I would get complete service hangs that lasted anywhere from 2-5 seconds before the signal would return.

The cause

Deco X20 will automatically swap devices on the network between the 2.4Ghz and 5Ghz bands depending on usage. When I would start playing a game or begin a call with someone, my usage was low - so my device would be running on the 2.4Ghz band. But as my usage went up the router would try to swap my computer to 5Ghz - which is unsupported by my PC and would cause service to drop

If your device doesn't support 5Ghz wifi, Deco X20 will still try to swap you onto it regardless

This causes your device to lose service until the router sends you back to the 2.4ghz band

In other words, the ping spikes were caused when the Deco X20 shifted my device that didn't support 5Ghz wifi onto the 5Ghz band automatically
 

The solution

In the router settings, you can set individual devices to use EXCLUSIVELY 2.4Ghz or 5Ghz. If you have a device that does NOT support 5Ghz, you MUST change the settings in the router control app (Deco app) to only use 2.4ghz - this will fix the problem for you

I wanted to post this here in the hopes it saves someone the 6 hours of diagnosis it took me to resolve this