get_the_post_thumbnail($post->ID, 'thumbnail'); not always returns the thumb size of the image (which is 100x100) for some posts it does but for most of them it doesn't. Even though the actual file exists (say for image
myImg.jpg there is a thumb image under the name
myImg-100x100.jpg) but still the function returns the full size.
any thought on troubleshooting this?
Update, I just noticed that the images that are returning the full size are named in Arabic characters, could this cause the issue?