I am having similar issues. I am using 3 Deco X20s, with Sky Q Main and Mini boxes connecting (to the deco network and each other) via WIFI. The deco mesh WIFI network was quick to setup and has been fast and stable for all devices apart from Sky Q.

On initial setup the decos caused both the Sky Q Main and Mini boxes to freeze and become unresponsive. Switching the decos to Access Point mode has stopped the Sky boxes freezing, but both the Sky Q Main and Mini boxes now lose WIFI connection frequently (despite the signal being strong at both boxes).

I believe the deco mesh network and the Sky Q mesh network are interfering with one another. I have experimented with changing the channel used by the Sky Q mesh; disabling the Sky Q 5Ghz channel; disabling the 'mesh' functionality for the Sky Q devices in the deco app, but the Sky connections remain unstable. 
 

What other actions do you recommend please @TP-Link_Deco ?
 

I did wonder about turning the Sky Q mesh WiFi off completely and connecting the Skq Q boxes to the deco network via Ethernet. This requires a deco adjacent to each Sky box, but this is not possible due to the layout of the house. Would a plug-in WIFI range extender (or similar) connect to the deco network and then to the Sky Q box via Ethernet please?

Thanks in advance.