According to wowhead, reddit and others a game master intervened in a +23 NPX and ported himself into the dungeon to kill some trash for the group who finished the last boss under %. The group is friends with the GM and were in VC at the time and asked for him to do them a solid.

All the details on wowhead, but this is wild. We can’t even get real people to respond to tickets but a GM has the time and ability to cheat in a M+ for his buddies?

Alleged Cheating in +23 Nexus Point Xe’nas Log - Wowhead News

Blizz, you cannot remain silent on this.

Game Master Intervened in +23 NPX