Hi mdzida
Sorry if my reply was not clear enough.
I did not mean that the menu is assigned incorrectly. What I meant is that you can test by assigning that menu item to 'Protostar' template - a standard of Joomla and see how it goes. The thumbnails are showing there.
But the style of this template override it so you don't see the thumbnails now, that's why I asked you to contact the provider of template.
I hope this make senses.