@SubscribeEvent
    public static void onAttachToEntity(AttachCapabilitiesEvent<Entity> event){
        if(event.getObject() instanceof Player player){
            event.addCapability(Helper.createRL("player_data"), new PlayerData(player));
        }
    }

public PlayerData(Player player) {
        this.player = player;
        this.setCurrentEnergy(this.getMaxEnergy());

 }

public int getMaxEnergy() {
        return (int) this.player.getAttributeValue(AttributeInit.MAX_ENERGY.get());
    }

and console log https://gist.github.com/MatyBotStorage/138473d7c4c7a43ad4b453baa4fda529

Why do you need a capability if you are using an attribute instead? You should not need to intermingle the two systems like this.