Anyone know how to stop the M9 Plus blocking access to PS4 online games?

Can access PSN, PS Store, download things etc but can't access any online feature of any game. 

If I tether to my mobile, works fine so it's not a PS4 issue, definitely at the home WiFi end of things (I'm assuming it's not an ISP issue for now). 

Deco M9 connected to Open Zone fttc modem. 

PS4 connected via WiFi to secondary M9 in the same room (full signal strength). Have also tried forcing connection to the main M9 via Deco app but same problem. 

Any ideas? Ethernet isn't really an option given where the physical kit lives in the room.