First off, this is a bug related to modding, but with that in mind, it's acting as a really weird hinderance for modders and mod users that I'm 90% sure wasn't intended when the Desync update was rolled out.

The game will crash other players if you're using a custom magazine and reload and vice versa if another player is using a custom magazine mod and they reload.

If:

• a custom magazine's part ID doesn't exist according you or another player, depending on who has and doesn't have the custom mag mod
  
  OR
  
  
• If all players have the custom mag, but the "uses_parts" index value for the weapon is different between them

the game will just leave an empty space in the 3rd person model for whoever didn't have the magazine mod with that specific index value. Didn't matter enough since it never led to crashing.

As of the Desync update, magazine dropping was added in and let's just say the game doesn't like trying to spawn in nothing. Players affected by the once minor bug above will be met with this in their crash log when the player(s) that has/have an invisible mag reload:

I found that two of the functions responsible for handing the dropped mag stuff, "anim_clbk_spawn_dropped_magazine" and "anim_clbk_show_magazine_in_hand", both in "HuskPlayerMovement", lack any fallback code when a magazine mod just doesn't exist for you or other players.