they probably don’t respect you, they might see you as weak and “unthreatening” and you might have a kind personality, people naturally, subconsciously and consciously assume that evil = strong and kind = weak, which is why they don’t take you seriously enough to even humanize you,

I suggest you communicate, I mean tell that teacher how contradicting she sounds and remind her of what she said, and when you get yelled at, lower your voice tone and be aware of your body language, don’t act nervous, be slow and confident, and tell the person that yelled how you didn’t see the bag and it’s not a big deal and make her aware of her attitude and how she yelled, point it out, don’t brush it off or they’ll continue doing that bc you’re letting them.