Confirmed, this is also happening on our server (1.14). I recently built a rail spanning 1100 blocks in the nether and encounter a few groups of Zombie Pigmen along the way. The areas I chose to kill the pigmen have not lost agro. When spending hours in the overworld (or other areas of the nether) and then returning to those areas the pigmen auto-agro without further engagement. This only happens for the areas I agro'd the pigmen. Other areas along the span of the 1100 blocks the pigmen are neutral. Other members of the server have confirmed this is all the case for them. If "Zombie pigmen are meant to stay hostile for 20 to 39.95 seconds" then that is not happening. I have even tried to kite them for minutes (without hitting them) to see if they will de-agro. They will not return to neutral.
Confirmed, this is also happening on our server (1.14). I recently built a rail spanning 1100 blocks in the nether and encounter a few groups of Zombie Pigmen along the way. The areas I chose to kill the pigmen have not lost agro. When spending hours in the overworld (or other areas of the nether) and then returning to those areas the pigmen auto-agro without further engagement. This only happens for the areas I agro'd the pigmen. Other areas along the span of the 1100 blocks the pigmen are neutral. Other members of the server have confirmed this is all the case for them. If "Zombie pigmen are meant to stay hostile for 20 to 39.95 seconds" then that is not happening. I have even tried to kite them for minutes (without hitting them) to see if they will de-agro. They will not return to neutral.