Certain photos do not display on the Roku's Plex App (gray screen with "Unable to Load Photo" error message), while others display fine. Seems to be all photos taken with regular point-and-shoot cameras fail, while pictures taken on a smart phone display properly. The same photos do not display a thumbnail, instead showing a gray square.
All photos display properly in Plex web app viewed from browser, and all photos happen to be jpegs.