This is probably just coincidence so don't take me too seriously but here's what I've noticed:
The professors of my biology/chem courses: "Hey buddy, don't be afraid to ask questions we've made sure to try and make things easy to understand. Here are some extra resourses for you if you're having trouble. We've structured the marking so that you have lots of opportunities to catch up if you have a bad week etc. Good luck! So proud of you all! 🥰"
The professors of anything to do with math or tech:
"LISTEN HERE YOU LAZY PEICES OF SHIT. IF YOU DON'T ALREADY KNOW EVERYTHING I'M SUPPOSED TO BE TEACHING IN CLASS THEN FUCK YOU. WE HAVE ONE TEST AND IF YOU FAIL THAT THEN YOU'RE FUCKED AND IT'S YOUR FAULT FOR NOT READING THE EXTRA RESOURSES I HID WITHOUT TELLING ANYONE THEY WERE THERE. WHAT? YOU HAVE A QUESTION? THAT'S A YOU PROBLEM, IDIOT! 
"
This true, professors make engineering/physics based classes horrible af and then bring up random questions of material never been spoken of before during the finals, and THEN pat themselves on the back when half of the class fails miserably, because their subject is hard or whatever.
I get accused of doing this when my finals are literally the midterm questions and assignment problems again lol.
I post a practice exam online a week before every math exam I give and I still get these complaints, so I'm definitely inclined to be sympathetic to the instructor without more information. It's like a student will memorize how to solve a problem from the practice exam involving sine and is now shocked to see the same problem with cosine appearing instead. We have never covered anything like this.
I had a much better experience when I was a student than most people seem to. I had a few professors who I had trouble learning from, failed classes with, but I really only had one professor who I thought was flat-out bad, a philosophy professor I took an elective with. Guy was a militant atheist and made it his identity, every lecture tied back to how religion is for simpletons. I've never really believed in anything but it felt very performative, like the focus was inciting someone to argue with him rather than to teach. Exams were multiple choice and all themed similarly, which made them easy 'A's by just choosing whichever option seemed most disrespectful. Attendance was a huge part of the grade and was a lot more difficult than the exams.
Yeah that's a big red flag right there
Sure that happens a lot, especially when students are missing classes and then complaining about not understanding the material haha. But there are some professors who like create exams that contain nothing and I repeat NOTHING that was taught all years long. This happened to me recently btw.
Fuck those teachers, I delivered a blank exam for my differential equations final because he barely covered laplace transforms a week before the final, and then he expected us to somehow be skilled enough to solve applied problems. I couldn't even parse the questions. Honestly I should've complained with the director, because this was just shit tier teaching.
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extra flair tbh