Thanks, Useless NPC. Yes, it's sad that this game is so bugged. It can be such a great game. And I hope (some might say it's wishful thinking) it can still be great one day.
Anyway, at long last I've managed to beat the missions as well as some of the challenges on Realistic difficulty, but it sure is one hell of a challenge!

I know how you feel, this happened to me a few times when I was going through realistic difficulty.