Description of the issue:

Whenever i drop a IE tool or weapon or put a shader on it all upgrades disapear from it there still funtional for ex. the extendet mag for the revolver but they are no longer shown in the Engineers Workbench.

As you can see the upgrades are still shown on the icon of the weapon itself but are not shown in the workbench.
Edit; when i click one of the upgrade slots the upgrade at least the extendet mag just dissapears and is no longer on the weapon.

Crashlog:

There is none it doesnt crash.

Versions & Modlist

IE: 1.16.4-4.1.2-129
Forge:35.1.34

I hope i could provide enough information thats all i got/found out.

Did you craft those items, or did you spawn them in? This is important because makes a difference to how their data is handled.

Also, please provide a debug crashlog by holding down F3+C for 10 seconds, because you have absolutely not given us a full modlist.

crash-2021-01-22_19.22.09-client.txt
The first time the items where crafted afterwards i restored them in creative everytime they vanished,
Also it seems to only happen in multiplayer.

This is likely a cross-mod interaction issue. I have so far been unable to reproduce this on my local server. If you can figure out which mod in your pack does this, that'd be great, but beyond that I'm afraid there's not a whole lot we can do.