So, I was doing some Cetus Bounties and suddenly,me and two of my teammates see this.
I wasn't quite sure, why this glitch would only happen looking into a certain directions, but after spotting a player name over the center of the disco-like effects, I realized it was Ecxalibur Umbra.
At first I thought that this might just be a client-side glitch only appearing rarely while Excalibur uses his Exalted Blade, I soon read complaints from my teammates about this Excalibur giving them Epilipsie (more than usual).
The Excalibur was completely oblivious what we were talking about, but we managed to convince him, to turn of his Exalted Blade.
Keep in mind that those glitches would change ever frame, but only if we looked at Excaliburs active blade.
Unfortunately I can't provide any footage, because I accidantely turned Nvidia GeForce Experience of instead of recording the last two minutes