most VDSL routers should support that feature. such as Archer VR2800.

a little confusing... You mentioned TL-WR7401ND like access point, and you still connect ethernet cable to WAN port with DHCP enabled on it? If yes, there is something wrong with your settings. you...

Which antivirus do you install/ it seems the antivirus affects the normal application. recommend you to uninstall that.

what's OS of your pc? Did you use the TP-link wireless utiltiy or windows utility? generally speaking, windows utility can help us connect Wi-Fi automatically.

How about the negotiation speed on the PC? change another wireless channel on your router. better to email tp-link support for further help...

Usually, we need to ping 8.8.8.8 when there is WAN IP address but still can't access internet. In this way, we can tell whether the current WAN IP is valid IP address or not. If we can ping it...