When you click "Launch" the game, the following notifications are popped up on the screen.
- Recommended settings updated
- Set optimal settings?
- GPU driver version
In all cases click "No" and wait until the game starts loading.
The game is still on the Beta phase, therefore, new minor updates are released a couple of times per day. This is primarily manifested in "Installing shaders to optimize performance during gameplay" notification. In general, it doesn't affect the gameplay, hence, it can and should be paused.
In this case, please choose any Warzone mode you are about to play.
Then click "PAUSE INSTALLATION" and go on playing the game :)
Pay attention that an issue in the game could be related to some temporary outages on the side of Activision itself. In order to exclude this case, please follow the link and check the status of their servers.