What do you mean “works fine when using WiFi” what is the other way you connect ?
Country ? ISP ?
try this 2 “basic+” things :
from link below Deleting Cache in WoW + Deleting only cache for Battle.net app/program https://eu.forums.blizzard.com/en/wow/t/comprehensive-guide-for-blzbntagt00000bb8-scan-loop-for-low-bandwidth-internet/416779
this command line will change your DNS server to all of your network connections:
WinKey + X => pick PowerShell (Admin) => write/copy/paste Set-DnsClientServerAddress -InterfaceAlias * -ServerAddresses 1.1.1.1,8.8.8.8
then enter => then write/copy/paste ipconfig /flushdns then enter
restart your modem/+router, fully disconnect from electricity for +30sec
try to disable all your anti-malware/anti-virus/firewall
Normally I use an ordinary wired connection through a router. I can use WiFi by using a WiFi dongle and turning off the Ethernet port that I normally use. I also use a free VPN for testing (TunnelBear).
Netherlands.
SURF B.V. Comes with the place I rent.
The fact that Wifi works, and the VPN sometimes works leads me to think some IP addresses are blocked server side for some reason, because each of these connection methods makes the server see a different IP address (and the VPN address probably changes sometimes).