Since the stout was fine, but the Black IPA was a problem, I would venture to guess that your pH was too low as a combination of adding gypsum to try to make the hops "pop" and starting lower with the pH, generally, between the two beers and possibly too large of a second batch sparge or too hot or a combination of both. That probably lent the acrid note from the dark malts and the astringency or overall dryness from a hot sparge. Try the recipe again using all RO water and inputting that 100% dilution ratio into Brunwater to work your additions.
Or I could be way off on the problem....