Larian Studios Forums Divinity: Original Sin 2 - The Modding Dungeon Divinity - Original Sin 2 - Modding Troubleshooting [Help] Custom Trader doesn't have custom items

I made a new trader NPC for my own Skillbooks.
The problem is, that the NPC doesn't have my Skillbooks unless you start a game from scratch, existing saves can't see the Books.

I made sure that the Skillbooks actually work, so the problem is the Trader NPC itself.
Any way to fix this?