Minecraft version: 1.20.1
Apotheosis version 7.4.3
Apothetic Attributes version 1.3.7
Obscure Api version 15
Moonlight version: 2.11.9
Target Dummy version 1.8.14

Armour pierce stops working if obscure api is also installed. Target Dummy mod was used to test damage values and was tested to show no sign of interference before adding obscure api. Other attributes including protection pierce remains functional.

Obscure API is a closed-source All Rights Reserved mod. No support is provided for these. You can see if they want to resolve the issue on their end.