I dont see any way the piglin could be getting killed
I had someone check in the box in spectator while I was down below, wither skeleton cant seem to reach the piglin and blazes dont even target them. Magma slimes cant spawn in the box and zombie piglins get filtered out through the corners.
I haven't spawn proofed the area around the fortress but im positive every block of the fortress thats exposed has a button on it. If blocks are above the fortress could fortress mobs still spawn there?
I dont believe any plugins could effect this either. All we have is maptool, and some kind of plugin that turns to day when only one person uses a bed rather than all players having to.
The fortress is in a soul sand valley as it said it should in the video. I guess this is because less mobs spawn there??? However, a couple blocks of the grinder are technically in a crimson forest but I dont really see how that would change anything.