Star metal mining with Acheronian pick gives 0 star metal

[Xevyr]

This is intentional, Star metal can only be harvested by a tool of Tier 4 or higher.

As you can see it was in the Chapter 2 patch-notes:

@Ignasi

Star Metal meteors are now again only harvestable by a tier 4 or higher pick, pick-axe or sorcery cull spell.