During the Halloween event, a portion of my icons on the hotkey skill bar and items appeared to fade out. All my skills and items were still usuable. (http://myu.icyworlds.net:4901/data/screenshots/155/19f53a19.jpg)
Inside the Forlorn Manor, the same thing happened to my inventory. (http://myu.icyworlds.net:4901/data/screenshots/155/32815483.jpg)
I'm not 100% sure on this, but I believe the glitch triggers itself when I use an item/skill. The skills fade out due to cooldown, but never fade back in afterwards.
It appears to only happen when I set my quality to Very Low. Changing it back to High does not fix the problem, however, logging in and out restores all the icons to normal.