Guild Wars 2

there is an animation, in the center (something that looks like electricity).
the longer you stay near it, it start to stack up(you can notice it on your screen), the animation objects are being recursively created which causes the fps to drop.

I take it this is the Song seal with the cannon event. This area has some kind of resource leak, causing the framerate to drop, even after you leave the seal area. The framerate is restored if you change map or re-enter via Character Selection screen.