Final Mission problems

Since the updates (DLC’s) I have had nothing but problems with the final mission, I have just played 4 HOURS straight and the Yuggothian will NOT expose itself at all? I have tried everything I can think of, but it will not? It used to rotate the shields and you could eventually get a shot in, it took a long time but you could at least do it. Now it just sits behind the shield and will not expose itself EVER!!! It drops the shields to do the mark of the void but closes them all after this, ALL the men die before you even get a shot off, WTF is that? Also 95% of all the spawned aliens are now zombies (as if it was not hard enough already) you just can not end it! I don’t mind a challenge but this is now beyond ridiculous. It is only by pure luck that I killed it the other times and that is not fun, that is just called frustration! SO… What’s the deal with the shields now? WHY do they not rotate, and it is not as if I did not give it a chance I think 4 hours straight of repetitive attempts to try and find a way is sufficient. Also there are some extremely irritating bugs that don’t help! 1: When you reload a mission OVER WATCH is disabled for the first round, you can not use it until you get to the second round, this can radically change the outcome. 2: The SPIDER MINES are constantly being eaten by the environment, I lost over 20 mines in the final mission to rocks and the ground just swallows them up, what is really frustrating with this bug is that you will place them and they are fine then you move them and go to place more in the the SAME place and they just disappear? So I had to keep reloading the game as I could not afford to lose the mines, very limited space for ammo as it is and this does not help that!