Popup shows in some product pages, but not in all

-- HikaShop version -- : 6.5.2
-- Joomla version -- : 6.1.2
-- PHP version -- : 8.4.24
-- Browser(s) name and version -- : any

Hi,

When showing products, sometimes they show in popup mode and sometimes not.
Where can I fix this, so that all products are (or are not) shown in popup mode.

The following menu-items show products in popup mode:
- Grote Readers
- Kleine Readers

All other menu-items show their products in the main window.

Hope you can help me out here.