EDIT: I managed to reproduce the issue once, here are some rough steps
Start the helicopters showcase.
Play the mission until you have to kill the two Hunters moving towards Mike-26.
After they are dead, the game will auto-save.
Allow yourself to crash into something and die.
Select the Autosave in the "load" menu, and see if it works.
Quitting to the main menu and returning to the game fixed the issue.