It was an interesting exercise for me because I knew nothing of the subject under discussion at all. Perhaps that made it easier to see where it was literally incomprehensible, as I had no previous knowledge to help me piece things together. I suspect the culprit was in the numerous drafts there had been, but some sentences were without verbs, and it mattered.
Also clearly visible were leaps in logic. These left me floundering, often due to going backwards and forwards in time, where a straightforward A:B:C:D would have been simpler. This happened, so that happened, so the next thing happened...
Stylistically I was struck by how many qualifiers were used, I assume in an attempt to make the writing sound more magisterial or academic. "Accordingly in all probability...However the general consideration of the facts in this circumstance...Arguably in these respects..." Nothing could be simply stated, all bets had to be hedged: generally, usually, possibly, sometimes, on occasion. Cut, cut, cut went my red pen. Also cut were repetitions and restating the case. I suggested adding several sentences too, for clarity.
The student thanked me politely, then a couple of hours actually looked at it because at that point another email came through: Bloody hell, mum, there's more red than black here. But he went through it, used some of my cuts and additions, rejected others. I read it again. It was the same, just better.
I've seen this before with student work. Careful editing doesn't change the writing, it makes it more like the writer wants it to be, cleaner, clearer, uncluttered. It's the difference between a dusty mantelpiece and one that's been cleaned, the bedroom after the bed's been made and the floor hoovered. The same, but better. And now it's cross fingers for the 1st.