This issue is caused by corrupted game client files.
To solve the issue you need to delete local settings folders. By default, they can be found here:
C:\Program files (x86)\War Thunder\Cache
and for Steam version:
C:\Program Files (x86)\Steam\steamapps\common\War Thunder\Cache
 
Also, please try to use "Check Files" option in the game launcher. It can be found in the sub-menu by clicking a gear button right to graphics settings.