I have a Mesh Router setup that consist of 6 S4's.  The first three were purchased together about 2 years ago and the others have been purchased as needed. We built an office behind our house earlier this year   The past few months the Deco's have continued to go offline intermittenly.    A few weeks ago I took two of them offline for testing purposes.  The issue still persist.  The main unit is the only one plugged in to my modem.  The others run wirelessly, with one providing ethernet connectivity to a PC.  The main unit is a v2.6.  The devices near it (tv, computer, ipad) work fine wirelessly.  I did notice the CPU is pegged at 100% in this deco.   The next closes Mesh router (v4.6) to it, is working right now.  All others are offline.   Sometimes, its a different router that is online instead.  Rebooting sometimes brings them back online, but that hasn't worked today. 

This setup as worked just fine for a long time.   I got tired of fighting with them and purchased a 3-Pack of Deco XE75 (TP-Link Deco AXE5400 Tri-Band). They haven't arrived yet, so I'm still fighting with my current setup.   Any recommendations or ideas on why the CPU is pegged?  They are all up to date on firmware, but some are different version of devices.