This behavior is related to the restrictions on the number of loaded pictures. We have a default restriction of 100 pictures, for better plugin performance. So the plugin is collecting specified images among the most recent 100 images from each of your sources. This limit can be changed by expanding the pictures limit. Go to the plugin Preferences page, find the Media limit field in API Settings (Advanced) section, and set the number you need. However, remember that when you expand the limit of images, it will affect the plugin’s loading speed. We do not recommend to set the limit over 500 images.