[unsignedint]

It might be because Nexus 5 is configured to connect through their IPv6 routing. (Not that viclone.com seems to have AAAA record, but it's looking like all traffic are routed through T-mobile's 6to4 so it might make a difference, too.)

[p1mrx]

It's a NAT64. 6to4 is for tunneling IPv6 packets over an IPv4 network.

[unsignedint]

Thanks for the correction. Those do get mixed up in my mind...

[andrewpi]

That seems to be the answer: if you set the APN on the Nexus 5 to IPv4, the site will fail to open, whereas on IPv6 it works.