Product list, some variation have picture some not

Dear Sir or Madame,

I have installed your plugin, everything looks good but on the product list some of the products show variation swatches and some not. If I click on the product there are some variation swatches so it is only a product list problem with your plugin.

Example:

https://www.equimunich.de/produkt-kategorie/pferd/

Please help me.

Kind regards
Lukas