I was standing around at ishgard yesterday just talking to another player without being in a queue or doing anything other then typing to him, and mid sentence it shut down completely.
Later on the same evening i was inside an alliance raid just before pulling a boss, and same thing there it just crashed as the timer was counting down, wasnt doing anything or pressing any keys.

So it just seems random? Sometimes im not doing anything, somtimes in a raid, or in a dungeon