To reproduce:

1. Create a course with a few activities or course sections.
2. Add some blocks to the course like the "Latest announcements" and/or the "Upcoming events" blocks.
3. Turn editing mode on.
4. Perform any course editing action that causes the course section or activity to be reloaded via AJAX.
   • Move an activity to the left/right
   • Hide/show course section
5. Turn on a screen reader (NVDA or JAWS).
6. Open the action menu and navigate through the action menu items of the edited course section or activity.
7. Expected: The screen reader will announce the appropriate names of the action menu items.
8. Actual: The action menu items become incorrectly labelled from items from other action menus because of element ID collision. (e.g. Instead of "Edit settings", it will announce something like "Configure latest announcements block").

This happens because the instance number that gets statically incremented is reset whenever the action menu gets reloaded via AJAX.