In at least some cases, zombified piglins that've been aggroed by a player fail to de-aggro even after the player has been hiding continuously for several minutes somewhere with no line-of-sight to the ZPs (which is several times the length of time it should take for the ZP's forgiveness timer to time out when it can't see the player, which is 55 seconds at maximum); I'm unsure what the conditions are to cause this to occur, but have found a situation where I can reliably reproduce it.

Steps to reproduce:
1. Unzip the file here into your saves folder.
2. Load the world stored in that zip archive.
3. Activate and go through the nether portal at 124/8/3.
4. Leave the portal's Netherside shelter and go to the cobblestone shelter to the north and about 30 levels up.
5. Aggro some ZPs.
6. Hide in one of the refuges in the shelter where nothing outside the shelter can see you.
7. Wait several minutes.
8. Go outside and walk around, especially in the flat area to the south or the steep slopes to the west.
9. Before long, you'll start getting chased by aggroed ZPs, even though the forgiveness timer on all the previously-aggroed ZPs should long since've expired by now.