I have discovered a bug that when trying to click on “Import or export calendars” it takes you to the “site wide” calendar management page, and you can’t edit a course calendar subscriptions.

if you click on a calendar within a course, it takes you to “calendar/managesubscriptions.php”

it should take you to “calendar/managesubscriptions.php?course=48”

48 being the course you where in when clicking “import or export calendars”

I did create a community report about this here

https://moodle.org/mod/forum/discuss.php?d=449178

Which has images and explains it a bit better.

If you wish to test:

1. Go into a course, expand the dashboard on the right, and add a calendar block within the course and then click “import and export calendars” and then import a course wide calendar. 
2. Once a calendar has been imported, go back into the course and click “import and export calendars” and you won’t be able to see the calendar you just imported