Hello
Maybe it is a bug. You will decide this.

I have Menu item connected with K2 Category called Instructions
In Instructions there are items which are from other categories eg. Materials - used option Additional Categories
In menu item options I am trying to sort items (ordering option) in FE display, but it mix items.

K2 gets from data base ORDER column and there are items with same values from different categories

Item form Instructions with value 1
Item form Materials with value 1
Item form Instructions with value 2
Item form Materials with value 2
Item form Instructions with value 3
Item form Instructions with value 4
Item form Materials with value 5
Item form Instructions with value 5

This ordering is displayed in FE

There is no option FIRST SORT BY CATEGORIES then sort items from each category.
It becomes a big mess

It is not possible to sort items with same values. There is no second parameter to sort - globally.

Hello,

If you want to use the sorting value across multiple categories, you should use "Featured Ordering" instead.