That user was me

It's not the DNS. Indeed changing the DNS did help, but after this I contacted my ISP. They use exactly the same DNS, and had no problem whatsoever. When I do a traceroute I can reach every hop, except for the last one. So, probably I am getting blocked, and it isn't a DNS problem. Also at the moments the website does not work, I can still ping it, which resolves to the correct IP.

But it is getting better, the site is working quite often for me now.