I often experience this problem.
I can log in to my account and access the character select screen.
When i choose a character i progress to the loading screen, and the loading bar fills up to 100%.
Friends see my model in-game and can see a message [xxx has logged in] but I'm still in the loading screen.
Either I stay stuck in the loading screen, but sometimes I am loaded into the game, but cannot see any other Players, NPCs. My friends/Guild list is also empty.
So far waiting for ca. 30 mins and attempting a new login with my fingers crossed has been only fix.