I was exploring a Piglin bastion and was killed by an invisble Piglin which I wasn't able to hit, or at least couldn't figure out where it was killing me from.
I arrived there twice, the first time I mined some of the gold there and I aggroed the piglins, I then was hit by an invisible piglin and quickly killed. At this point I had full iron gear with no enchants but had gold boots(although that shouldn't come into effect as I had aggroed them).
The second time I arrived I had a iron chestplate and was 1 hit killed by the invisible piglin, I swung wildly a couple times before but couldn't connect any hits. I'm also not sure if the piglin should have deaggroed after my death or if the aggro should continue over.
I have the newest version of optifine (the 1.16.1 3rd preview) installed.
I've seen 2 other Invisible Piglin issues brought up but neither mentioned being 1 shot even with a chestplate, normal difficulty, I may simply not be used to there hits or that could be another possible bug.