I have been playing DU since its launch and never had issues with it. Maybe I was just lucky, maybe there is indeed a glitch that I somehow managed to avoid. Anyways, here is what I figured out to be always working to get an A+ in every course in any of the degree programs (always taking 4 courses in a term x 3 terms):
① Make sure all the relevant skills are maxed out manually (meaning without the help of cheats/mods) before you enroll. In addition to the major skills (i.e. cooking, painting etc.) I always max out on writing and research/debate since they appear to be adding some bonus whilst studying in general.
② Make sure, there is no CC in any form or shape in your game since, as someone pointed out a while ago, CC computers/laptops may be corrupted (turning in papers or asking profs about progress might not work properly). In addition, I never use cheats/mods in order to alter progress or generate needs/moods
③ Enroll on a Friday so you can finish all your homework, papers and presentations (with "excellent/outstanding" quality) during the weekend and deliver them asap (even before the message "A new term has started" appears on Monday morning). I do hand in the papers on Sundays, presentation boards on Mondays if there is an open time slot.
④ Attend every class with "Take notes" attitude
⑤ Never spend time to study extra hours (not even if the class concludes with a final exam). I usually spend the hours prior to an exam going fishing with a friend. 😉
This procedure has become so much of a routine to me that I play it in 3x speed without ever having problems. And most importantly, none of my Sims had gotten any grade other than an A+. As I said, maybe this works only for me but I'd be glad if some poor Sims out there get the grades they truly deserve. 🥳