Daikin U5 Fault driving me crazy

Last year we installed a Daikin FCAG125BVEB with a WiFi adapter and madoka controller, since then we've had nothing but trouble, the latest problem being a recurring U5 fault, we've replaced both the indoor pcb and controller and the fault keeps coming back, even ran the controller cable in separate trunking to make sure there's no interference, any ideas will be greatly appreciated

What type of cable have you used to connect the controller?

1mm 2 core flex, ran in trunking, no more than 10 meters

Shielded or unshielded?