Wish I could help you.
I've had the same thing happen to me: I'll go months without any trouble, and then I'll go to load a saved game and it stops at the "a long time ago' screen. Then I'll try loading the save before that . . . and before that . . . and before that . . .
Any more, once I start a mission, I never exit the game until I'm back in base, just in case. I'll put my pc in hibernate to save power when needed, but I won't ever again exit a mission until I'm safely docked.