Upgraded to 2.9 today. I'm using the Magazine Template as my home/front page (I created a page, then Settings - Reading - Static).
No sooner than I upgraded then, that home/front page now shows up in the Featured Content slideshow, and I can't get it out of there. No, that page isn't toggled in the Featured Content section. To double check it, I created another page, switched it to the home/front, and sure enough, that page started showing up in the slideshow.