I am aware there is a tiny bug currently known where when breeding Flapple and or Appletun the egg will produce a child of the same evolution instead of Applin. However in the case of passing down HA abilities, while Flapple still has that 60-80% chance, Appletun seems to be a 0%. When breeding 5 Flapple Eggs from a HA Flapple and a Ditto, 3 of them were HA. However no matter the method (HA Appletun x HA Appletun or HA Appletun x Ditto) more than 20 eggs were tested and not 1 HA passed down. The HA ability Thick Fat as a HA does pass down with other pokemon, such as HA Alolan Rattata. But as for Appletun, it does not. Thank you very much.

Fixed for upcoming I believe, I'm getting H/A applin from breeding Appletun with thick fat. If this is still a problem next update make a new ticket. Thank you for reporting