Don’t forget that you’ll have to populate the inventory array like you did when it was in the player character.
You can use a PrintString node to test the state of your methods at various stages to track down exactly what problem you have.
For example, just after you set the ActiveGameInstance variable in your character, pull out a PrintString node and print the value of ActiveArmourID and ActiveWeaponID, then change the values and print them again. If everything prints out correctly, your game instance is working fine and the problem is somewhere else.
You can go through your execution sequence like this and find where the problem(s) occur.