variants display incorrect in dropdown

-- HikaShop version -- : 4.2.1
-- Joomla version -- : 3.9.8
-- PHP version -- : 7.2

When displaying variants for a product with a dropdown, too many variants are displayed. If table is selected in stead of dropdown it displays the correct variants.
For 2mm we have 3 options, for 3 and 5 mm just one... dropdown shows 3 options for 3 and 5 mm as well...

Any idea how to get the correct items in a dropdown?

thx in advance.

There is no option to do that.
It would require adding javascript code to the product page to dynamically remove the elements from the other dropdowns when you select something in a dropdown.