Hello @Dimme
If the device has connected to Wi-Fi of extender but can not open certain websites, you could try to manually set up the DNS settings for that device.
- For IOS device, go to Settings > Tap WLAN> select t of extender> Tap Configure DNS> Manual > Key in DNS 8.8.8.8 ; 8.8.4.4
- Configure DNS for Windows PC as Step4-Part2-2) https://www.tp-link.com/support/faq/41/
For Smart TV bad signal, it could be caused by the limited Wi-Fi bandwidth
It is recommended to put RE in the halfway between router and Wifi dead zone, How to place your wireless Range Extender for optimal reception and performance
Connect to 5Ghz Wifi band of range extender if TV supports 5Ghz
Or try to wire your TV to the range extender via Ethernet cable and see if the connection gets better?