I have the Spring theme for Upfront and use the Posts List.

Hi!
I have the Spring theme for Upfront and use the Posts List.
My problem is that the Posts List displays only resized full images (eg 250 Kilobytes) and not real thumbnails (eg 15 Kilobytes).

The Featured Image of Post list contains following code:

<div class="uposts-part thumbnail" data-resize="{{resize}}">
	{{thumbnail}}
</div>

How to get real thumbnails?

Thanks!