Sometimes the Group Search opens above where the groups are selected and the search bar doesn't come into view and you can't access it because it's above the page. I have to drag it over to a larger screen so it expands below and the search bar comes up. It woudl be helpful if when you click on Groups, if it always opened below. See attached pictures.
Depending on viewing size of screen will sometimes put group filter above which makes it hard to select.