I found that for a certain image size on my site, all the images in the library were greyed out. Turned out that this was fixed if I unchecked “Crop thumbnail to exact dimensions (normally thumbnails are proportional)” in media settings. Didn’t see this documented and the solution may not be immediately obvious to all, and may conflict with a desire for exact dimension thumbnaiils.
Are you trying to set the min/max to the exact size of the image you want to display on the front of your site? What type of values are you putting in for min and max?