Some players are currently facing Call Of Duty Warzone dev error 6634 on PS4, PC and Xbox One. Some players also getting Warzone dev error 5518 and error 6347. Activision is aware of these issues and working on them. A minor hotfix is already released. However, players still facing these issues.
According to the game developers, an issue (Warzone Dev Error 6347, 5518, and 6634) is causing hang crashes on the GPU. Players are also facing disconnection and login issues.
A fix for the above issues is coming with the upcoming update. Also, check Warzone servers status here.