Puzzle:one of my best presentations

There is a function in Libreoffice Impress,the presentation(.odp:or open document presentation)-specific app I have used in Ubuntu for as long as I can remember,and love it,like most things Ubuntu uses and popularises(when I used Windows,I used MS Powerpoint,but I am not a fanatic by any means),and this is a nice utility,slide sorter that allows looking at the format of the entire presentation.

Now I am creating a presentation from a flap-based report from 2008,and I use like always,as a template,one of my best past presentations,which I gave at the AHS Forum in 2011,which was in Virginia Beach,Virginia[https://vtol.org/who-we-are/our-history/listing-of-society-forums].
This is a screenshot of the slide sorter,and I am wondering why most of  the plots after slide 9 are boxless,like a ravenous mouse set to having a lunch of this file 😎😄😈😇...