Me and another FC friend are also suffering from the same issue and its rather irritating as we cannot join rest of FC in the dungeon.

My details
ISP BT
Connection fiber
speed 25Mbps download 18Mbps upload
character aetherial flow
race miqote
world aether cactuar
class/lvl BLM 50
Solo
NPC G'rahna Tia
Steps:
1. Right click on G'raha Tia
2. No quest dialog pops up.