Very little fraying at the tail ends of the lines exercise, nice going! Scrolling through the exercises, it almost seems as though your confidence in creating strokes and lines decreases the more complex the homework gets. Everything up until the boxes/perspective exercises feels loose and confident, which is great. Is the focus on the requirements for perspective perhaps drawing your concentration away from making those clean, loose lines?

I already said this to someone else as well, but as you are really good at creating those kinds of lines between two points, maybe plotting the corners of the perspective boxes down on paper and then drawing lines between them (for the short term until you feel more confident) help convey more confidence in box drawing?

Then again, we gotta dive head-first into that 250 box challenge after this, so it might not matter...we'll all have perfect boxes by the end of that!