What is this floating green light in Vah Medoh?
Wherever this light is coming from, it is a glitch, and has nothing to do with the dungeon at all.
As for what it might be, the animation is far too fast for it to be the light from Satori Mountain, and comparing it to the updrafts, it has a similar speed to that (although the more magical appearance obviously shows that this isn't an updraft).
The game is known to experience a variance of graphical glitches, across different platforms, so it's not entirely unexpected, but at the very least it's not game-breaking.