yep it seems to be iiNet IP's only (well one one TPG range) in the 203.x x.x range and from what IT looks like it is a routing issue in the USA where they host the site.
I have a ticket in for it with iiNet (who i work for) to try and see if its us or somewhere between us but to me it looks like the Scubadoctor Webhost (in the US) is treating traffic from the 203 range differently from other ranges.
so far testing shows
Not working from
iiNet office Subiaco (iinet) 203.59.x.x
iiNet office Subiaco (iinet staff BYOD- this is the work wireless for non work devices ) 203.59.x.x
iiNet manilla call-center (tpg telecom ip ) 203.213.x.x
My connection (iiNet consumer) 203.59.x.x iiNet business grade static allocation
and works from
Optus mobile 49.196.x.x
TPG corporate (tpg telecom) 202.7.x.x
Telstra (mobile) 1.127.x.x
Internode (technically still IiNet but the range is not a 203.x.x.x) 150.101.x.x static allocation Ip
Exetel (i don't even know who they are) 58.96.x.x
If you want to add to this info for me as ill be letting Scubadoctor know so they can bring it to the attn of their provider
the following will provide me with nearly anonymous but relevant information
1) google "whats my ip" and that will tell you your public IP
2) then put that into the search field at
https://dnslytics.com/ip
-- when you do that about half way down the page it will tell you who owns the IP range that your IP is allocated from
for example.(this is my work machine)
ASN name (ISP) iiNet Limited
IP-range/subnet 203.59.128.0/17
203.59.128.0 - 203.59.255.255
3) and post here the ASN and IP-range info