Hello,
When is selected for ex: Thumbnail format [jpeg] and i upload a png file to the product for the ex everytime when system won’t to acce the thumnail will not found it becouse it search for [color=#ff0000]if (!file_exists($th_path)) {}[/color] on fn.images.php on line 1006 on v2.2.4 in our case will search for something like this [color=#008000]/images/thumbnails/x/width/height/image.png[/color][color=#000000] and the[/color] the is not normal there becouse is saved as [color=#008000]image.jpg[/color] and every time is accesed the thumnail he will be done again and loading time is increasing dramatically.
Sorry about my english, i hope this will help to make make the best ecommerce solution out of CS-Cart 
Have a nice day everyone.