Zero from the megaman series is the source of this glitch. He has a hyper combo that makes a clone of himself and copies any move the original Zero would do. So technically whatever you do with Zero will happen twice having like a small delay between the attacks. Theres also a thing called a snapback where you use one level bar to snap a character out of the screen switching to the next character. Little tactics to bring out those beaten characters that another player is trying to recover.
the Zero Glitch happens when you do a snapback with Zero's Super that i mentioned. If the original Zero's snapback misses and the clone's snapback hits, No character will return leaving the other player to lose from time out. Bummer, i know. Why does it need to be addressed? well because it could happen intentionally or accidentally during a fight. Watch and see the glitch in action.