After Optus finally found the issue with our realy lousy cable Internet service (including replacing the modem) there are a few websites which we cannot connect to. The best example is paypal.com.
To prove that I am not going nuts I used my Ipad which connects wirelessly to our network and also has a 3G SIM card.
I can't get paypal whist on the network, it times out BUT I can connect on the 3G connection.
@ozxanadu, am I correct to presume that you're in NSW?
I replied to a similar thread → https://yescrowd.optus.com.au/t5/Broadband-Telephony/PS4-Can-t-connect-to-network/m-p/394127#M49756/...
I've left a little explanation if you're interested to find out more.