I have the same problem, but as the Russians on the defense. What is really annoying is that my guns get knocked out every time, and usually I don't even know what hit them. Is line of sight not reciprocal in this game?
Here's an example. I had an AT gun BEHIND a building, in a spot where it had no line of sight to the approaching Germans, and it was pointed northwestward. There was a German tank approaching, which my infantry could see. My gun was in a perfect spot...I had the fire command ready and was waiting for the tank to move up just a few meters...when suddenly, BAM, my gun is hit and destroyed. I have NO IDEA what hit it. It was as protected as it could be...behind a building. I don't see how it could have been the tank, because how could it have seen the gun before the gun could see it?
I'm quite frustrated because all of my AT assets keep getting destroyed, and ATRs don't work well at all. I'm stuck on a particular scenario which involved defending against a lot of German armour...once my AT gun is gone, the battle is pretty much over.