What kind of SW are you using for the VPN ? Have you tried to connect with another device (mobile phone, tablet, etc.) to these websites, are they displaying correctly ?

Since when this issue manifested itself, any changes on the router configuration/ISP service prior to that ?

@Betovanbuuren Have you observed the logs of the router, anything suspicious in there ? Factory reset via WebGUI or by the reset button on the back of the router ? It is recommended to hard reset...

@Betovanbuuren How do you connecting to your ISP - directly (PPPoE, Dynamic IP, etc.) or ISP modem/router before your router ? You can try to change the DNS settings on your devices (for example try...

Give some more details on the issue. Have you observed the router logs during the disruptions ? Did you check if the AX20 is overheating ? What's your connection to the ISP - direct (PPPoE, Dynamic...

You can try this image for EN version: https://static.tp-link.com/res/down/soft/TL-WR940N_V3_150312.zip