Honestly, I'm baffled as to why this happens, but I'll explain what I experienced.
I usually play chronomancer and I've been using DX11 as to try it out, and besides a few crashes here and there (probably things that other people have reported, such as a fractal DC that my teammate also had) it's actually decently stable for hours and hours.
So I decided recently to start playing a mirage build, and to my surprise, every time I turn it on, I don't last more than a few minutes, sometimes even seconds, before GW2 instantly stops responding and freezes, up to the point where I have to shut it down manually. In terms of addons, I actually had ArcDPS and it ran fine when I was on chronomancer, but I also turned that off when switching to the mirage build and it still freezes, it's unplayable - I had to revert to DX9 to play for more than a few minutes.
Any other mirages having this problem with the new DX11? I'd love to know if this was on my side only, possibly some hardware involved or something, but I'm really enjoying the DX11 improvements and this kinda bums me out to have to revert to DX9.
Cheers!