The same thing happened to ours about a year ago. I was told that sometimes the manufacturer cuts the opening for the windshield a little bit to large. I was also told to keep that from happening again I needed to be more careful when leveling so that the frame doesn't flex.
Now when I level, I plant all 4 jacks firmly on the ground with just enough pressure to slightly feel the coach move. Then I raise the coach with whichever pair of jacks is needed to get the coach level.
This seems to be keeping the frame from flexing, because I haven't had an issue with the windshield since I started leveling this way.
hotjag1
2003 40' Allegro Bus, 3 slides, 400hp 8.9 liter ISL Cummins
2000 24' Dynamax Isata