I've been dealing with a reoccurring issue with modded weapons where modded sights don't work, causing the gun to ADS like it has iron sights, and not though the sight, not sure whats causing it.
You need Custom Attachments with Custom Weapons to get custom optics zeroed properly for custom weapons.
https://modworkshop.net/mod/19169
Still having the problem after installing the mod, and I think i had in installed anyway
What custom weapons are you encountering the issue with and what custom animations/viewmodels are you using?
If you're running some sort of Perfect Viewmodel presets mod that touches ADS stances, there is a decent chance there's issues here.
The only other issue I can think of is if you're running a weapon based on the reload M4A1/CAR4 animations (Pawcio's HK416 or Carl's AAC Honey Badger as examples), but then run Fnuxray's hold animation which swaps the hold animation of the M4A1.
If you still have the issue, I don't know how else to help you since most custom optics and custom weapons get their zero from dropping in CAFCW.
i had that issue with one of the guns in the "Vanilla mod pack" mod idk why it happens but when i used a vanilla sight it worked fine so it might just be something about the sight pack. Which one are you using?