Problems with Powerpoint for Mac

First of all, I am running MacOS 10.13

I recently created a presentation on Powerpoint for Mac 2011 (v14.0) and although I had no problems creating it, after I saved it and re-opened it, all the thumbnails were upside down. The slideshow plays normally (only the thumbnails are upside down).

I am also having a great deal of difficulty moving slides around in the presentation, as I don't seem to be able to drag-and-drop the thumbnails the way I should be able to.

I tried quitting and restarting Powerpoint, as well as restarting my Mac but nothing seems to help.

Is there anyone who has any idea as to what might be happening?