Multi-Reference only displaying some possibilites to choose

Hi I currently have one collection called “partners” with all kind of infos about partner shops (logo, name a.s.o) and I wanted to have a Collection called “categories”, added there a multi-reference for the corresponding shops that belong to the specific category.

My “partner” collection includes 219 items.

Problem now is:
When I try to add partners to a category, I cant choose from all database entries, just a few of them. It also starts the list from the middle like the letter “m” instead of “a”. Is that a current limitation or a bug?