Summary: Cannot show block on userpage just by setting visibility to ‘user’.
Solution: PHP snippet on block visibility.
I had the problem outlined here on Stack Exchange. In particular, setting the block to display on /user only did not work.
I found the solution here, which shows the block on the user’s page, but not on other pages (e.g. user/1/edit etc.). Another important link in the chain was this comment to enable PHP in the block visibility settings:
First, enable the PHP filter module and give yourself permissions to use PHP in order to input PHP on the Block visibility settings page.