Splitting wifi - not applying setting

[Box104]

I have followed the instructions to split the Wi-Fi to 2.4GHZ and 5GHZ. When I untick the 'synchronize 2.4 and 5' box, rename the WiFi and hit apply, it says 'page won't load'. When I log back in to the router the tick box is still ticked (ie setting not applied).

Anyone know how to resolve this?

Sky technical team won't assist as they don't advise to split the wifi