A - There are no net issues, they're simply slow.
B - There are net issues, within the player's own network.
C - There are net issues, within the player's ISP network.
D - There are net issues, somewhere along the route between the player's ISP and the last node prior to the FFXIV's data center.
And less likely, as it'd involve many more players:
E - There are net issues, within the FFXIV data center's ISP.
F - There are net issues, within the FFXIV data center.
G - There are net issues, within the player's specific server clust / server / however hardware wise SE has hooked their systems up.