There are a few reasons why you'd get this kind of behaviour. First check is that DNS is working (should be 18.104.22.168). If not you could try adding a static entry on your machine, or change name servers. Various DNS servers have non standard configs that make things break in weird ways.
Check you can reach the IP. It responds to ping, but somewhere its setup is strange because it drops a lot of packets when pinging from different places at once. Put the IP in your browser - it should redirect to a web hosting page. If you can't reach the IP it's probably some routing issue somewhere between your ISP and the server. You could try a traceroute and see where it gets stuck (not that you'd be able to do anything about it, but at least it would give you some kind of diagnosis).
The info in the link appears to involve changing your IP, which would obviously help if you've been IP blocked (I don't know how likely that is).
Or, just do the challenges at work