(I've edited my original post and added this there, but just to reiterate for people who may have not seen it):

Unfortunately my Network Engineering friend was unavailable during the weekend. I have logged a ticket with the 2degrees Network Operations Team (NOC) and let them know it looks like an MTU issue (and have linked them to the Whirlpool forum post where their Network Engineers have fixed the issue for their customers). Hopefully the NOC team will pass the ticket to the Network Engineers first thing Monday and we can get this resolved.
For players in NZ with 2degrees, if you contact them you can reference ticket #: INC0604594.