Crazy, after 9 years.
I can see all my (7) courses in the Garmin Connect web AND app. When I create an event, such as a race, the dropdown course box only shows four of the courses, and I can't select the other courses. I tried making them favorites, which didn't help.
I saw one older post suggest there was a page menu, and that resizing the window in Chrome (I tried Chrome, FF and Edge) would force the UI to show the course pages, but that was an old post and it didn't help.
Maybe it's an imported course? Like in this thread: Why does a course need to be public to add to a private event?.
Thanks. That was a good possibility. I am new to Garmin, and I did import the course from a Polar GPX file. There were actually two issues in the course settings. First the public/private has to match the public/private setting of the event, which was easy as you get an error (not very prominent). The second setting is that for the imported course, the course type was blank, and needed to be set to (in this case) running to match my event. Between the two things, that fixed the issue.