[Gen 7] Gen 4 starter's hidden ability not passing down?

I have an Empoleon in Ultra Sun with its HA that I got through a wonder trade. It’s almost certainly not legit, as it is LV 100 and shiny, but I believe it’s legal as it has passed through the Bank without issue. I was hoping to breed some HA Piplups, so I bred it with a Ditto and hatched a bunch of eggs. The Empoleon is male, so I was expecting a 60% chance of HA passing down when paired with Ditto, but after hatching more than 25 eggs I’m getting the non-hidden ability every time. I guess technically I could lose the 60% RNG 25 times in a row but that seems really improbable.

Is there some lock on inheriting HA from a non-legit Pokemon? Is there some other mechanic in play that I’m missing? It’s not a huge deal but I’d just like to figure out what’s going on.

Edited: spelling

Pleaselog inorregisterto add a comment.

Alright, I know this is old but I wanna get this off the unanswered list.

It’s almost certainly not legit, as it is LV 100 and shiny…

That is an important part of this to note to those of you who haven’t read the entire question.

The asker of the question has said:

Apparently it is possible, with hacked/genned Pokemon, to merely change the ability to the HA without changing the underlying data that is passed down through breeding. So although the summary page for the Empoleon shows it having the HA, when breeding it is passing down its original, non-hidden, ability. I have no experience or interest in dealing with the programs that allow you to see or change these things so I can’t confirm, but this seems the most likely answer as statistically it’s nearly impossible to not get the HA after that many attempts.

This is most likely the case here, though we can’t know for sure.

There is also the slight chance that this is just awful RNG, but I doubt that.