You haven't said how you have connected the switch - ideally should be router - switch - everything else connected to switch. Also switch and router may have certain ports dedicated to connect to modem/router etc only. If the switch is in between one PC and the other, it probably won't work.
Also not sure how the Sky Q router handles DHCP as WiFi wise I believe they act as a mesh network (if you have the second box or more) , know of people who've had issues trying to mix and match other wireless APs with Sky Q ones.