only small res picture of adaptive image system is cached

Hi guys,

I use the Uncode theme for WP with an usually well working Adaptive-Image-System.
When WP Fastest Chache is active, only a small version of certain images is cached and therefore displayed for every page visitor. When disabled everyting works fine: Images are first displayed in low res and after loading the full res image, it is shown immediately.

Help is very much apprechiated.

THX Milwa