It first started to happen with the DirectX trouble (1100002 something), at first it was more a non-updated video card driver problem. So i updated them and it stopped for a while (maybe a month or so?)
But it came back, so i uninstalled everything with the local files deleted also then reinstalled everything... didn't solved the problem.
The multi-crash with no error message have been happening more lately since 4.5, 4.5.BLU.

There is no pattern to the crashes, i tried to go underwater, to go in the sky, to change location, to do Raids, dungeons, anything up to chocobo races, and it still crashes.
I'm running out of option, as i write, i just crashed again. It can happen in loop, or it can happen after a few hours.... really nothing for me to guess it right now...