Hello  @Robo1984 

May I know the build number/ firmware version of the AP, please confirm TL-WA901N V6  is already on the latest firmware which released in 2022( for EU version). 

It's good to know that you've tried some steps like testing the router Ethernet connection, resetting the AP. 

• Please also try a different LAN port on the router 
• Try a different cable between Access Point and router (Ethernet Led on WA901N should be ON)
• Make sure other network devices can get internet from the same Ethernet cable (with Wi-Fi disabled on the laptop)

If you have tried the above steps but issue persists, I'd recommend reaching the retailer to check the warranty first. As the AP has been worked for a pretty a long time, you could get it a replacement and see if the replacement unit works as usual.