Plein Air Painting and Cast Shadows

The biggest difference between painting on location (en plein air) and painting in studio is the time management. Although some painters (like Monet) go back to the same location multiple times to finish one painting over days and weeks, most plein air painters spend about 3 hours to finish a painting. Within those 3-hour painters, a portion of them put in finishing touches in their studios. Many develop a larger studio painting based on the smaller plein air pieces, field notes, and their memories. I've made multiple-day plein air paintings, not by choice, when I was in class and ran out of time. But I prefer to finish the damn thing on location in one sitting and move on.

Painting en plein air in winter is especially tricky though, because within 3 hours, the direction of cast shadows shifts close to 60°. You have to decide when to switch from painting what you see to painting what you remember. To me the switch usually happens midway through the 3-hour session. If I don't make the switch, I end up making a painting like this:

Hanger on Desire Street
oil on canvas, 16"x22" (2013)

The cast shadows on the ground were painted early on, and the shadows of the two rooftop chimneys were put in near the end of the same 3-hour session - duh!
This will never happen in a studio, unless you're making a surreal painting that purposely messes with perception.

The painting below was done in about 3 hours in a strong wind, while shivering and saying hello to the passersby and security guards. I was also under at least 8 security cameras.

French Quarter Alleyway
(or Askew Light Post Named Wallace)
oil on panel, 8"x12" (2018)

The red and yellow buildings in the background stayed lit in the same way the whole time, but the brick buildings on the left went from dominantly-in-shades to completely-lit by sunlight. The top of the shadows cast by the tall buildings on the right side (off the frame) was at the third floor level of the buildings on the left when I started. But within 2 hours or so, the sun moved (or I should say the earth turned) to where the top of the same cast shadow was on the sidewalk. I decided that the top of the cast shadow should be in the middle of the light-green doorway, and lined everything up accordingly.

Now the question is, what made the top of the light post askew in real life while the rest of the post stayed straight?