Hi,
We had a lot of freezing rain today followed by rain and wind. The wind was strong and blowing almost directly into the corner in the picture. For a while I was getting water on the floor on the other side of the wall in the picture without a door. It was entering behind or underneath cupboards on the wall (and floor) a little closer to the corner than the range vent.

I checked the attic on both side of the wall and found nothing? Any suggestions? How is it getting in.

Floor is level with the door in the picture.
Vent in the picture is for a range hood.

Give us a close up picture of the flashing detail where the single story shingles meet the vertical wall. Can you write a description of the construction detail in that area?

For one thing, you appear to have no gutters. For another, I see snow piled against the house in the corner. Both or either of those could be contributing to the problem.

You are missing the kick out flashing on the wall where the soffit meets the larger wall. Water almost always comes in at that point.
Simply put the flashing detail is incorrect.