Before I get to the critique, I just wanted to mention that a mistake in one instance is not a big deal - no need for apologies or explanations. We have students complete a large volume so that patterns can arise and suggest misunderstandings or incorrect approaches that we can then explain and address. Similarly, the point of the challenge is not for you to come out the other side drawing excellent cylinders - each exercise has its purpose, and sometimes (as I'll explain later when we get to the cylinders in boxes) the purpose is not always obvious to the student as they're working through it, and so it's best not to give your own expectations of what matters and doesn't matter too much weight, and focus instead on just following the instructions to the best of your current ability. As long as you do that, you'll be fine.

Jumping in with the cylinders around arbitrary minor axes, overall you've handled these pretty well. Early on I did see some cases like 2, 5, 15, and 25, where you were drawing the side edges of your cylinders as being parallel on the page (something that is addressed as being incorrect in these reminders), but you stopped doing this pretty quickly and fell more in line with the instructions. I also noticed that early on you were drawing those cylinders smaller on the page and not quite making full use of the space available to you, but you addressed this yourself and by the end you were using that space quite well.

Aside from those points, your work is coming along well - your ellipses and edges are confidently drawn, and you're quite meticulous in checking the true alignment of your minor axes.

Continuing onto the cylinders in boxes, you handled these very well. 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.

In applying those line extensions thoroughly and correctly throughout the set, you armed yourself with plenty of useful information on how to adjust the proportions of your boxes so that the ellipses' contact points line up better with the boxes' vanishing points, which in turn gradually rewires your brain's understanding of the relationship between those proportions on the flat page, versus what they represent in 3D space.

All in all, very well done. I'll go ahead and mark this challenge as complete.