.
Can you create a 2.4GHz only network on your UniFi AP and connect the Q box to that. In theory it should work fine with a combined 5 & 2.4GHz network but the reality can be quite different. As far as I remember you can only use 5GHz Wi-Fi on a Sky Q box if you're using a Sky router.
I'd be inclined to do a network reset on the Q box, connect it to a 2.4GHz only network from your UniFi AP and go from there. If you've moved all your devices over to using your UniFi AP then could you disable Wi-Fi on the Sky router?
Indeed.
@PahuljicaZ
I have my Sky Q boxes on my UniFi 2.4GHz IoT SSID.
Sky router stayed in its box.