Mysterious red doors have been appearing in Verdansk since the beginning of Call of Duty: Warzone Season 4. Stepping through one will teleport you to a random loot-filled room—or, since the mid-season patch, to another part of the map, although it wasn't immediately clear whether that was intentional or a bug of some sort.
Not long after that update went live, players began encountering behaviour that was definitely not intentional, but unfortunately very familiar: The red doors are now turning players invisible, a bug that should be familiar to Warzone players.
As you can see in the video below, the glitch is both simple and tricky to pull off: You have to pull and prime a grenade, hop on a motorcycle (Kotaku says an ATV will also work), and step through the door, basically all at the same time.
It's not an overly complex instruction set, but the timing has to be spot-on.
Warzone developer Raven Software has struggled with invisibility issues for months. The Season 1 update in December 2020 added attack helicopters to the game, which enabled players to make themselves invisible; in March 2021 they were finally brought back, but the next day they were gone again when it turned out that the problem hadn't actually been fixed.
It's not clear whether this is the same bug with a different trigger, or an altogether new issue, although it doesn't really matter: Players are getting hosed by people using this exploit, and the game is suffering for it. Here it is from the other side of the coin—as you can see, it sucks.
I've reached out to Activision for comment, and will update if I receive a reply.