An orphan room can be created when either all users in the chat room are banned, or when all users in the chat room are deactivated and there is no owner. If either of these situations occur, the room will be deactivated and become an orphan room.
Note: Banning a user is actually 2 actions, removing the user from the room and blocking the user from being re-added by the owner
If a user is experiencing an error stating Cannot add member to a deactivated room, it is possible they are trying to add a user to an orphan room. To resolve this, a Super Compliance Officer can unban the user and add them back into the chat room, as long as another user has been made an owner prior to this.
Note: Currently the only way to make a user an owner of a deactivated room is to use APIs to promote the member outside of the user interface
Refer to the Knowledge Article found here on how to deactivate a chat room, or use the block feature instead of banning all users, as this is less likely to result in an orphan room being created.