Hello Community 
I changed the logic of my setup and followed this tutorial to replicate the character materials. It works as the host, but not as the client (print string are the same on both, but materials won’t change in the client).
Here is my setup:
The struct is saved in the SaveGame and is loaded into the PlayerController:
SaveGame
PlayerController
The FirstPersonCharacter (BeginPlay) calls the event to get the struct and sends it back to the PlayerController after loaded:
FirstPersonCharacter
The PlayerController then sends it to the GameMode (onServer):
PlayerController
The GameMode is looping through each registered PlayerController and calls them to Initialize:
GameMode
The PlayerController casts the struct to the FirstPersonCharacter and calls for the setup:
PlayerController
FirstPerson (onServer)
FirstPerson RepNotifier
Example of RepNotifier
Can anyone tell me where my mistake is? 
Many many thanks!!