It's exactly that: the difference in generations can result in close matches of one tested person showing up as distant matches in more 'recent' (further removed from the common ancestor(s)) relatives, like you would be to your father's aunt.

Having them not match at all is also common and expected. The recombining of the DNA each generation can either 'trim down' segments that these relatives match you on, but they can also cut them out entirely.

Let's say your father's aunt is on his mother's side, i.e. the DNA you and she share came to you via your paternal grandmother - the DNA segments she has in common with those matches may not have made it to you. It might have been swapped during recombination for a piece of your paternal grandfather's DNA, or even from the opposite side of your paternal grandmother's side of the family.