hmm ... that's because those images are smaller than imagevue thumbnails and Imagevue is set to not scale smaller images.
Are you looking to display the thumbnails scaled up to default thumbnails size, or do you want to display the thumbnails at the same size as original then?
Sorry for the late reply - I have made a fix for this. Please download the following file: https://www.photo.gallery/down/getfile.zip
Unpack, and replace the file "getfile.php" with the one that is in the Zip file. It allows you to display the smaller thumbnails.