The application became unresponsive and was terminated by the OS.
An “Unusual process exit” message is displayed by Arma 3 Launcher whenever it detects that the game was not closed correctly. That may mean that the Operating System (OS) was unable to start the game or that the game has crashed.
The exit code in the message is a number provided by the OS and it may be ambiguous. However, it still may provide a clue about what the issue is and how to solve it.
If you need to, you can copy the message by pressing Ctrl + C while it's displayed, and then paste it to the Feedback Tracker or another channel by pressing Ctrl + V. https://community.bistudio.com/wiki/Arma_3_Unusual_process_exit