"Despite the continuous declaration that posts related to this one are duplicates that have been resolved, there is a consistent trend that it is currently implausible to lose Zombie Pigman aggression after they are attacked from one of many different possible sources. This issue has been observed in the 1.14 Pre-Releases, among other snapshots."

Couldn't have said it much better myself than this quote of a previous report. That report was listed as "RESOLVED." Why? It's not resolved - it's bugged. Stop confusing people thinking it is not broken. I just wasted a few hours trying to remove the permanent aggro in my hardcore game thinking I was doing something wrong. 

Are there any commands I can use to reset the aggro? I will never hit another zombie pigman again after this.

Thanks and have a good day!