Starting with your cylinders around arbitrary minor axes, you've done a great job. Not only are you consistently executing straight lines that are smooth and consistent, and ellipses that are evenly shaped (suggesting solid use of the ghosting method), you're also checking your alignments fastidiously, identifying even small deviations - the sort of thing that can cause a student to plateau as they get into the "close enough" territory, if missed.

There's one quick point that I do want to draw to your attention, but it's only something that came up very rarely - be careful when it comes to drawing your side edges such that they run parallel on the page - basically eliminating the foreshortening altogether and forcing that vanishing point "to infinity" in the manner discussed in Lesson 1. The thing is, we do not directly control where the vanishing points go. We control how we want our form to be oriented (and therefore control the orientation of all the sets of parallel edges that make up our form), and it is that orientation that dictates where the vanishing point should be.

The only situation in which a vanishing point would go to infinity is if the edges it governs in 3D space align perpendicularly to the viewer's angle of sight - basically, not slanting towards or away from the viewer through the depth of the scene, just running straight across their field of view. Of course, given that our cylinders are rotated randomly throughout this part of the challenge, this would be all but impossible.

Like I said - this was barely present in your work, but I did see it, and I wanted to make sure that you understood this concept.

Moving onto your cylinders in boxes........ Damnit. So I know I just said that the issue I spent the last couple paragraphs explaining was barely present in your work, but perhaps I should have looked through everything before I started writing. Unfortunately, no time to change my phrasing now, as this is my last critique for the day, and I've got a steak dinner getting cold on the table.

The issue is that you appear to have specifically forced your boxes' vanishing points to infinity. While I cannot speak to your reasonings for this, I can certainly understand the desire to take what is admittedly a rather challenging and time consuming exercise, and simplify it by avoiding having to worry about the convergences and just keep everything as parallel as possible. Unfortunately, as explained above, this is not just a bad idea - it's functionally incorrect, as far as perspective goes. What you're going for here is a sort of 0 point perspective, which simply doesn't exist. There are other kinds of projection that are more similar to this - isometric/anomoetric - but they have entirely different goals from perspective projection, which seeks to replicate human, bifocal vision.

Ultimately, this exercise is really all about helping develop students' understanding of how to construct boxes which feature two opposite faces which are proportionally square, regardless of how the form is oriented in space. We do this not by memorizing every possible configuration, but rather by continuing to develop your subconscious understanding of space through repetition, and through analysis (by way of the line extensions).

Where the box challenge's line extensions helped to develop a stronger sense of how to achieve more consistent convergences in our lines, here we add three more lines for each ellipse: the minor axis, and the two contact point lines. In checking how far off these are from converging towards the box's own vanishing points, we can see how far off we were from having the ellipse represent a circle in 3D space, and in turn how far off we were from having the plane that encloses it from representing a square.

Given that we don't have any convergences in your boxes, this renders this approach a lot less valuable, and unfortunately that does mean you are going to have to redo this section of the challenge. I'm sorry to be the bearer of bad news - but while 100 cylinders in boxes is by no means a small ask, it is a temporary thing, and you will get past it.