I've built the afk pigmen farm by ilmango. It's exactly at max. height and I assume it's exactly the same as his.
Pigmen spawn without problem and I do have in total 12 pigmen around with name tags on them.
However, after about 30 seconds the pigmen spawning don't seem to care about me until I move around or shoot some newly spawned ones with my bow.
Why is this and is there a way to change it?
1.13.1, Spigot server with default config.
If you've not already seen it, Minecraft 1.13 - Gold Farm Aggro & Baby Fix may be helpful…
There was at least one previous discussion of this issue… but it, too, seems to have been removed in The Great Purge…
The base problem is that [unannounced/poorly documented] changes in how the aggro chain propigates were made in [more than one version?] of 1.13, breaking the original farm (published 28Sp17).
WARNING: I have an extemely "grindy" playstyle; YMMV — if this doesn't seem fun to you, mine what you can from it & bin the rest.