Thumbnails are not displaying

Hi,

I’m using this shortcode [wp_rss_retriever url=”https://feeds.feedburner.com/vceliste” items=”5″ excerpt=”none” new_window=”true” source=”false” read_more=”false” thumbnail=”30%” date=”false” dofollow=”true”], but the thumbnails from https://vceliste.cz/blog/ are not displaying. I have access to vceliste.cz so I tried to install this plugin also on that website but it didn’t help. I also tried to install the Featured Images in RSS for Mailchimp & Other Email plugin, but still no change.

Any idea how to fix this?

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