Can't access a website, thinking router issue

Alright so this had me stumped today... site in question is:

https://essentials.myob.co.nz

ISP is 2talk, UFB 100/100, router is Mikrotik. VEEERRY basic network. Single site, three PC's, three IP phones, Unifi AP.

Basically, loading just hangs, and then eventually errors out.

Troubleshooting I have done...

- Client was using Chrome, so firstly cleared all cached data - no change- Tried an Incognito window - no change- Flushed DNS, 'ipconfig /flushdns' - no change- Tried on IE - same issue, no change- Tried on another PC with all of the above - same issue, no change- Tried on my laptop - same issue, no change- Jump on router, flush DNS, flush DNS on PC - no change- Change public IP address, flush DNS, flush DNS on PC - no change (we are a 2talk reseller so can manage the connections ourselves)- Jump on to a terminal on our head office network - site loads no problem- Try on Spark mobile data - site loads no problem

So this leads to me think I have a router config issue. We run a rubber stamped config for all our routers, and just modify where needed. This site has zero changes to our standard config - a config deployed on 200+ routers.

So i default the router, reload a new config, issue is still there.

So now I wonder, is the issue with the UFB connection itself? I haven't pushed this to 2talk support as I want to keep working on it for a bit.

My quick work around for the client was to just set them up a VPN out through a different connection, that will suffice for the short term.

What do you reckon?!