@Kevin_Z 

Thanks for getting back to me Kevin. The Decos are AC1200, m4 and the extender is a WAVLINK WL-WN570HN2 outdoor extender.

The Decos work well without the extender, and most often with it running, however at times they do seem to drop out entirely when I change settings on the extender. It's intermittent though and I can't seem to nail down what makes them drop out. 

It's a very basic home network. ISP router Ethernet to main Deco, Extender Ethernet to Deco. All clients are configured through the Decos. I disabled WiFi on the ISPs router but it's still functioning as a router. I tried running it as a bridge and using the Decos as the only router to avoid double NAT but once I do that I lose connection with the ISP. I called them to work with them and they said they don't support that mode so I guess I'm stuck running it as a router. It works great though except getting signal through the extender.