Joseph's shiny new sketchbook

[Who]

Lovely cast drawing for sure. I think you're right, the figure's far arm looks weirdly stunted. It's possibly the difficulty of the unfortunate angle. I've experienced the same thing, where something is drawn accurately, but just looks wrong in the drawing. "never let accuracy get in the way of a good drawing" is the way I've often heard it explained. As the Atelier you are at seems to go for a highly accurate observed approach, anything that doesn't really lend itself to a good drawing I guess isn't allowed to be discarded or artistically amended, and so the smallest "deviation" from what you actually see can cause cascading issues because the tolerance level for "errors" or deviations is much lower. Does that make any sense in your specific context?

To me it looks like the elbow or what appears to be the elbow of the far arm appears much higher than it should be if it was vertical. If that arm's elbow was more sticking out away from his body, that could suggest potentially the arm is not foreshortened convincingly in your drawing. It also makes a self contained shape that tangentially sits on the chest instead of feeling like it connects to something. Perhaps a bit more introduced atmospheric perspective on that arm would push it back a bit more into space too. You could also look at introducing some variation in the shadow values of that arm. I feel that the mostly single value creates a too unified separation between chest and arm which draws a lot of focus to it.

The near arm isn't as bad, but there is some legibility issue with the wrist area, and perhaps again tweaking the foreshortening so we really feel the elbow coming more towards us might help.

But yeah it's all good. Fix it till it works, or take the learning and move on, no big deal either way.