It’s a DDOS attack on DynDns, which provides DNS services for a ton of sites. I use it myself because I got tired of keeping my own DNS running in the face of waves of reflection attacks, mostly from China. They do it to shout down political sites that the don’t like (I think).
It was just too much of a hastle to change my firewall filters every day. I suspect a lot of big sites outsourced to DynDns for the similar reasons and to save money on IT personnel.
These sites maintain (or should) a fallback DNS server on site with a short TTL as a backup - optionally turned off until it was needed - with its NS record sorted last.
This is the reason for the slowness. Your DNS query has to walk through NS1, NS2, NS3 (which are all down) until it reaches to fallback server NS4. This can take several seconds or a minute depending on your ISP’s DNS forwarder timeout settings.
Oh and that’s per query. A lot of web sites today are pretty complex and fetch a lot of queries for image subdirs (images.foo.com), script subdirs (scripts.foo.com), CDNs, etc. So yeah it can take a long time. Just be patient and the web page should eventually appear.