Why is window cracking?

I’m looking for some thoughts on what might be causing my Andersen window to crack. This is a double-hung window and it is the upper section that cracks. I already changed it once and it cracked again. I did some reading and found that it might be a thermal stress crack due to temperature changes. The house is a raised ranch and the window is in the lower section of the knee-wall in the middle of the house. The house does get a lot of sun, but there is a bush in front of the window and there is also 18” overhang for the upper section of the house. I mention this since articles about thermal stress cracks state that shadows and heat transitions are the cause. I also read that there is really no way to stop this from happening. In any case, before I change the window again I wanted to get some different opinions.
There is another thing that I was thinking might be causing the issue. When the window was installed it was secured from the outside using the flanges on the window. However, on the inside it was also shimmed on both sides and the top since pine trim jambs were needed to accommodate a 2X6 wall. I checked and the shims go all the way in the gap against the side of the window and not just where the pine jamb was added. So, could it be that the window being shimmed is causing the problem and not allowing for expansion and contraction? Should Andersen windows be shimmed at all on the inside? I know the shims are needed behind the pine jamb, but these shims go all the way in. I can send pics if needed. Thanks