i have been sometimes experiencing this issue, it's like this: at random moment game changes to a black screen. If I open up the task manager it says that the program is 'not responding' and I have to force-close it. Last time it happened when i was hitting Dark Falz in his first form. So far experienced this issue only on character slot 1, maybe because I mostly play in that slot. Biggest minuses of this situation are: that you leave your teammates in a disadvantage, and what's more important the EXP, weapons and other things aren't saved, so when you comeback your character will be in the state before connecting to that session you had the Black Screen of Death. How the Black screen looks? ALL pixels turn black, though the BackGround Music will still play.
Additional info:
Guildcard: 42148568
Time when issue occured: ~20 minutes before I wrote the post. TTF counter was at ~31 minutes.