1) Double-check to make sure that you're right about your Pokémon's IV's.
2) Double-check to make sure that the parents are holding the right items.
3) If you're sure nothing wrong, I looked around and found sites with contradicting conclusions about whether Power items could be used with Destiny Knot of not:
Pokemondungeon.net [link] & A user from Pokecommunity.com [link] states:
"You cannot use both the Destiny Knot and the Power Items" & "The Destiny Knot and Power Items do not work together, the effects are not combined," respectively.
A Neoseeker.com user [link] argues that:
"...so this definitely confirms that the Destiny Knot will not override the Power items. However, it remains to be seen if the Power items override the Destiny Knot," which means that Destiny Knot will not nullify Power Weight's effect.
After browsing the internet, many sites refute Power items and Destiny Knot's ability to work in tandem, while many others state that it's possible. So it's very possible that Destiny Knot and Power items don't work together, but in the end, the right nature is more important (imo), so perhaps you should give the male an Everstone to hold instead until you manage to breed another male with more perfect IV's.