REVIEW THE GUIDELINES - see Contributing link on right side.

Minecraft version:1.12.2
Galacticraft version ("latest" is not a valid option):
GalacticraftCore-1.12.2-4.0.2.280
Galacticraft-Planets-1.12.2-4.0.2.280
MicdoodleCore-1.12.2-4.0.2.280

Single player (SP), Multiplayer (MP), or SP opened to LAN (LAN)?
Single player

Any Galacticraft add-ons installed? Please list all of them:
None

Please upload crash report / full log to Github Gist or any other paste site:
No Crashes

Please provide screenshots / videos / full modlist as needed
Mod List:
GalacticraftCore-1.12.2-4.0.2.280
Galacticraft-Planets-1.12.2-4.0.2.280
MicdoodleCore-1.12.2-4.0.2.280
mw_2.0-0.4.4.6_mc1.12.2

Please state the site that you downloaded Galacticraft from:
https://micdoodle8.com/mods/galacticraft/downloads

This probably happens because of Galacticraft using a custom player model.

Screenshots:

item is not where it should be

same with thermal armor (and oxygen mask too)

we can see that its in its right place IF you were standing

Crouching is broken too

NOTE: You need to set allowEmmisiveItems=false in forge.cfg in order to use vic's modern warfare.

EDIT: The hitbox DOES change

Both Galacticraft & Vic's Modern Warfare Mod change the Player and Player rendering. Didn't look too promising when seeing it also doesn't run on a certain Forge version (very old version) unless 1 of 3 solutions is done, as well as being a closed source mod it pretty much puts it on the level of Optifine when it comes to compatibility. Closing this as Will Not Fix.

Appreciate the response. Maybe mention it on https://wiki.micdoodle8.com/wiki/Compatibility ?