NextGen Gallery Plugin - Edit Thumbnail Crop Not Working for 240 X 160 Thumbnails

With Wordpress 4.7, Atahualpa 3.7.24, and NextGen Gallery plugin by Imagely Version 2.1.62 --

The plugin's Edit Thumbnail function under Manage Gallery is not working for 240X160 Thumbnails to display the re-cropped thumbnail in the Gallery.

Says "Thumbnail updated" and shows the re-cropped version in the back-end under Manage Gallery. But, when I click "Save Changes" and then go to the published Gallery and refresh, the old Thumbnail (with people's heads cut off) still shows.

Is anyone else having this problem? Is there something special I need to do besides: set the default thumbnail size under Settings, and then go to Manage Gallery, click "Edit Thumb," select area for the Thumb to display from the picture on left, click Update, exit pop up and then click "Save Changes"??

Will appreciate any help!!