Just open any save and enter the Nether, use a spawn egg, naturally generated or structure-generated Piglins, stand there for a while and you'll notice them turning into Zombified Piglins.
In fact, these piglins should only transform in the Overworld and the End; in the Nether, they cannot turn into zombified variants. This bug is really outrageous.
（Piglin brute generated by structures or spawn eggs will also transform into a zombified piglin in the Nether, but I think these two are the same bug, you can track them together.）
Linked issues
is duplicated by 22
MC-303139
Piglins will be zombified in the nether
Resolved
MC-303146
Piglins zombifying in Nether
Resolved
MC-303156
Piglins turn into Zombified Piglins in the Nether
Resolved
MC-303179
Piglins, Piglin Brutes, and Hoglins zombify in the Nether
Resolved
MC-303185
Piglins and zoglins automaticly turns into zombie form in nether
Resolved
Attachments
Comments 4
TheUranusCU2888
In case you didn't know, hoglins also have a mechanism similar to piglins; they can also turn into zombified versions in the Nether (zombified hoglins can now naturally spawn, which I think is a good change, even though it's technically a bug).
I believe this issue is caused by the new addition of the “Environmental Attributes” in this snapshot. The patch notes show that there is a “piglins_zombify” attribute which is set to true by default. My guess is that the developers forgot to set this value to false in the Nether.
Patch notes: https://www.minecraft.net/en-us/article/minecraft-snapshot-25w42a