@Unlucky345 go into the Netflix app and find tge network test in the Get Help menu and let it run. You need a steady 25Mb/s to becable to watch in UHD and it is likely that the wifi connection to your hub is not delivering that. Check your hub is in the best position which is out in the open on a surface above obstructions like radiators. The same applies ti your.Sky box avoid tge temptation of tucking it behind the TV which blocks a lot of the signal.
Beyond that you may need an extender or similar if using an ethernet cable is inpractical.
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65inch Sky Glass, 3 Sky Streaming Pucks, Sky Ultrafast + and Sky SR213(white Wifi Max hub) main Wifi from 3 TP-Link Deco M4 units in access point mode
