Some apps not syncing over Virgin wifi - LG G2

A

AC Question

I'm having issues with Facebook, Instagram, Google Play and Photos (backup) not syncing over a Virgin wifi network - some aspects of the apps work fine, for example Instagram will update with comments, likes etc, but I can't upload pics, same with Facebook, and photos won't autobackup, the sync process seems to start but freezes. Other applications, such as Mail and weather update perfectly.

Any ideas? The phone works fine on all other wifi networks, and also on mobile data alone, which indicates possibly something wrong with the wifi network itself, but I don't know where to start..