https://techcommunity.microsoft.com/discussions/sharepoint_general/picture-libraries-not-showing-thumbnailsimage-preview-fails/29969
Picture libraries not showing thumbnails/image preview fails | Microsoft Community Hub
Picture libraries don't seem to be working. No thumbnails and when I click on an image I see the attached message. This happens for .png, .jpg,...
picture librariesmicrosoft communityshowingthumbnails