Hi  @zivkovic,

If the Internet on the router is working fine but you cannot visit a certain website or use a specific App, please review the following troubleshooting steps: 
    1. Connect the client device to a different network or mobile hotspot to test the connectivity of the App/Website. 
    2. Check if the App/Website works on different devices or web browsers. 
    3. Power cycle the router and the device. 
    4. Log into the router's management page via tplinkwifi.net, go to Advanced > Network, and change the router's Primary DNS to 8.8.8.8 and Secondary DNS to 8.8.4.4. 
 

When the router is working in wireless routing mode, have you tested the speed?

May I know if your network topology diagram is as follows,Is the modem still running wifi?

Cable modem—router )))((( client devices

(Note: — stands for wired connection,)))((( stands for wireless connection )

 Hey @Joseph-TP,

Troubleshooting steps:

1. Yes, everything works when connected to ISP Modem wifi or to LTE.

2. Currently tested only on two phones (Iphone X and Nothing phone 2), both have same issues with youtube.

3. Power cycled it a few times already, no change.

4. Current DNS settings are set to cloudflare (1.1.1.1 and 1.0.0.1). But I will test google dns servers as well.

The speed of the device on wifi is maxing the provided ISP speed (500/100 Mbps). This speed was reached on both router modes (access point mode/router mode). Router was configured as router mode by default and then later switched to access point mode.

Yes, the network topology is as you said(Cable modem -> cable connection -> tplink router -> wifi -> wifi clients). The modem is still running wifi, but the modem is on the ground floor, where the router is on 2rd floor (modem wifi is not reachable here), so no wifi conflicts can exists (also both wifi are on different channels). Modem also provides only 2.4Ghz wifi.

Thank you and best regards, Jan