In this thread, I've already pointed out multiple times, what the problem probably is - and where the troubleshooting should start. VPN is a good workaround for everyone obviously, but it still has nothing to do with DNS.

To be clear: If I use the same DNS Servers on my VPN connection that I use on my ISP direct connection, the problem should stay if DNS was the issue. But it isn't staying. I can use the same DNS Servers on VPN and it's fine.