As another user has stated above me, the latest update for the Canvas teaching app for IOS, which went live last Wednesday, broke the annotation tool. I have been in contact with support but no solution has happened yet, and I'm sure I'm not the only user that this is affecting critically. Clicking the brush/pen tool for annotating no longer works if a student submits more than one file on an assignment. It works on the first file, but once you navigate to the second or any other subsequent file the brush/pen tool no longer works. So for now, until this is fixed, the annotation tool is broken, and cannot be properly used as described above.
This discussion post is outdated and has been archived. Please use the Community question forums and official documentation for the most current and accurate information.