I also have a professor who is experiencing this, exactly as you describe. I also cannot replicate the issue. Did you find any solution?
They are not selecting the wrong tool in the toolbar. They select the "hand" and the PDF moves around. They select the "arrow" and the PDF moves around. They select the "annotation tool" and the PDF moves around and annotates as it goes.
We are on Moodle 3.4.3.
- Stamps - using the Apple Pencil, stamps appear below and to the right of where the Pencil hits, i.e. the top left of the stamp is where you placed the Pencil. You can get used to this, but wouldn't it be better for the center of the stamp to be where the stylus is placed?
- Annotating (lines, circles, etc.) - if the PDF can scroll, it will scroll. Thus, the only way to draw a circle is to have the pdf scrolled all the the way to the top, place your stylus, and draw a circle UP (the PDF cannot scroll up). Or scroll all the way to the bottom and draw a circle DOWN (the PDF cannot scroll down). Same with lines.