It has been now several weeks that I work on the PE1. I find it harder to fully straighten my left arm. In the beginning I found it hard even to just rotate forwards the left elbow pit. That has improved much. Still it seems that I need more effort to keep the left arm straight, and at rest the left elbow pit is less rotated than the right one. The right wrist is also more mobile: I can manage more wrist bend on the right (around 90 degrees between palm and forearm feels fine) than on the left (around 5 degrees less I think).
The wrist position in this element, and in stretch 2, feels fine in my right wrist, but it is uncomfortable for my left one, which feels sore, especially towards the thumb side of the hand. The soreness disappears shortly after I stop doing the stretch/exercise.
I can perform the mastery number of reps, only my left arm is not always completely locked, and the left wrist angle is less than the right one (so to have proper contact with the wall I need to keep my left arm slightly towards the right). I am wondering if I should stay with PE 1 until I resolved the imbalance, add supplementary work for the left side, or start working on PE2/PE3 hoping to get a quicker adaptation of the left wrist.
Last thing: several years ago I had a left wrist fracture. I do not remember exactly what I fractured and it never bothered me so I am inclined to think it is not related to the problem, but if you think it could I can check what exactly happened.