Well, in my case it's all even more complicated. In part of image carousels pictures are displayed properly - in some other image carousels pictures are blank (white boxes). And there are some mixed cases - some of pictures in image carousel are displayed, but some others are invisible, and that's really confusing. Let's say there's image carousel made of 3 pictures - and I can see first 2 of these pictures, the last one is blank.
Video carousels all are blank. Ugly scroll bars appears also in other elements - like the collections of Story on the account main page (if there's a many different collections in it). Videos in carousels still can be watched through Page Info > Media > Video link.