Thumbnail are not shown for newly uploaded images

1. Login to CMS, navigate to Images folder
2. Upload a normal image and view it on left pane (Reading Pane)

Actual Issue - Thumb Nails are missing except for the variants "thumbail" and "orginal" (refer attachment)

3. Select a image, click edit and crop one of the thumbnail image (example - thumbnail small)
4. After cropping click "OK" button

Actual Issue - Thumbail is not save, I see "error occurred, please retry". I have attached the exceptions in file.