So I had a problem with shadows appearing where they shouldnt. When I attach the vanilla model to the custom one, either the smoothing breaks or the shadows appear instantly. Attaching the models in ZModeler doesn't mess up the quality, but sadly I can't get a new license right now.

How it looks: https://imgur.com/xXt3dyP

How It's supposed to look like: https://imgur.com/JOVfRHC

This only happens with that piece of gear in the picture. The vest is a task_000 while the belt is a accs_000. The pattern changes as I change the accessoire. It look like the normal map of the accessoire is somehow placed on the vest and creates the weird dots and lines.
Bug:
https://imgur.com/xydtXqu
Correct:
https://imgur.com/zUqyVxZ

@borrie Discussing online-modding is forbidden here.

@s3xyman11 Are you using a mods folder ?

@matysop https://forums.gta5-mods.com/topic/14693/quick-start-guide-to-modding-grand-theft-auto-v/2

@StreetRatKnight @EugeKill Have you tried installing the OpenAllInteriors mod and enabling the MP map in the .ini file ?