I'm not exactly sure how making hangar repair occur works.
That said, what size is it? For whatever reason, fighters aren't tended to by maintenance facilities at all, so it's gotta be above 500 tons to get maintained, or just kept inside hangars in the first place.
But yeah, if you didn't put them inside a hangar immediately as soon as they were built, then the destruction was likely to happen. If that's not the case, however, then something else is going on.
As it is, if you can't find a way to repair fighters using shipyards or hangars, then it's best to just scrap them and replace them with a new batch.