In 1.17 there was a change to AI that removed the ability for entities to target an Armor Stand that is either: Invisible, Invulnerable, or a Marker armor stand. If the Armor Stand has even just any ONE of those qualities it will not work at all.

While this may be functioning as intended, datapack developers use armor stands very frequently for their projects, especially Invisible and Marker armor stands, because they limit player interaction while still retaining the functionality of an armor stand. Invulnerability is also useful because it prevents it from being killed by other features of your datapack as well.

I am reporting this as a 1.18 issue because the 1.17 changelog makes no mention of any changes to AI.

To try this for yourself use 1.16.5 (Working) then 1.17.X / 1.18.X (Not Working)
You must first summon either target for the Piglin to path to, then edit storage data and copy the UUID of the Target back to the Piglins' <angry_at> parameter.

1. /summon pillager ~ ~ ~ {Tags:["TARGET"]}
OR
1. /summon armor_stand ~ ~0.2 ~ {Tags:["TARGET"]}

2. /data modify storage minecraft:target data set value {Inventory:[],Brain:{memories:{angry_at:{value:1}}}}
3. /data modify storage minecraft:target data.Brain.memories.angry_at.value set from entity @e[tag=TARGET,sort=nearest,limit=1] UUID
4. /execute as @e[type=minecraft:piglin,distance=..48,team=players] run data modify entity @s {} merge from storage minecraft:target data

You can get a better demonstration of what I am trying to explain by watching my video here.

Please consider datapack developers with regards to reverting this change. Unfortunately there is no workaround for this.