So I was making a car, but I couldn't move a vertice. I saw that someone else had said this question and one person said to turn off proportional editing. But when I tried it wouldn't turn off. I unchecked the box that said proportional editing, but when I came back to make sure it was unchecked, it would still be checked. EDIt: It if off, but when i move any edge, vertice, or face it automatically turns on.
I think the real culprit might be the Mirror option under the Options dropdown in each viewport.
I have no idea why it's sometimes turned on, maybe a cat walked on my keyboard. But when random vertices are moving when I don't want to, it's usually that. It needs to be turned off for every object individually.