I tried it out successfully on my end. I must have keyed something in wrong. I made a button that created a collection with similar structure below
ClearCollect(colEmployees, Table({Name: "Joe", Title: "Manager", Department: "A"}, {Name: "Mary", Title: "Director", Department: "B"}, {Name: "Tom", Title: "Manager", Department: "C"}, {Name: "Joe", Title: "Manager", Department: "C"}))
And then Filtered it in a gallery.
Filter(colEmployees, !IsBlank(Name) && !IsBlank(Title) && Department in ["A", "B"])
Regards,
Pat