If you are a COD fan and play the game regularly, it is impossible not to play the DMZ mode. Released with Warzone 2, the DMZ mode has created its separate fanbase, and players love the faction missions. However, DMZ mode is not exclusive to Warzone 2 players; like other features, MW2 and Warzone 2 share this mode and maps. So, regardless of the game you have purchased, DMZ mode is available to all.
DMZ mode has several POIs, and Building 21 is one of the most popular among them. It was introduced as a separate map in DMZ mode and is accessible from both games. Building 21 is a small regular building like you have encountered in Al Mazrah, but this building is rich in loot and enemies. However, Building 21 is unique because it can be accessed during weekends and requires its key to be accessed. The key to Building 21 must be collected from Al Mazrah or Ashika Island maps.
Since its launch, Building 21 has frequently disappeared due to bugs, and players have recently reported that Building 21 has disappeared from Warzone 2. Modern Warfare 2 players accessed Building 21 this weekend, but Warzone 2 players couldn’t. This has created dissatisfaction among the Warzone 2 players, and they reported the issue to various forums and even to Activision Support.
Activision has recognized this issue as a bug and updated it on their Trello Board. On the contrary, on Reddit, someone shared a post where Activision Support said that Building 21 is permanently removed from Warzone 2, and players must purchase MW2 to play Building 21.
It created more confusion among players that whether they really have to purchase MW2 to access their favorite DMZ map. However, primarily players believe what Activision has said on the Trello Board that it is a bug and they will soon fix it. There are missions related to Building 21 which stopped progressing because of the bug. Warzone 2 players can do nothing until the next weekend comes. Only then can they check if the bug is fixed.
That’s all you know about the issue of the disappearance of Building 21 in Warzone 2. It doesn’t seem logical to remove the map from Warzone 2, so it is definitely a bug and will be fixed soon.