I had this problem occur over the weekend. This happened in 2 of my 3 current courses. I edited an announcement I'd previously created and got the message about send or just save. I chose to save as I'd set the announcement to delay sending and it would be weird for my students to get an announcement that an announcement they'd never seen was changed. The delayed date has now passed for all the courses, and I only received an email for one of the courses. I can see that all three announcements are visible on the homepage and I'm now wondering if my students in the other classes received an email of the announcement.