[1.14.4] Data stored with my custom capability attached to player doesn't seem to save data into NBT

In an attempt to learn the capability system, I made a custom capability that tracks a simple variable
(called counter) and allows me to increment it by 10 everytime I right-click with gunpowder and right-clicking in the air will print out the current value to the console.

The incrementing and printing out works fine.

However, upon rejoining the world or respawning, the value in counter resets back to the default 20. From my limited understanding of capabilities, this must mean the data is not being saved as NBT so there's no data to load for respawning or rejoining. That or a new instance of the CustomClass class is made overwriting the previous one? Btw I do have a player clone event method.

Here's the code:

CustomClass

public class CustomClass implements ICustomClass {

    private int counter = 20;

    @Override
    public void setCounter(int value) {
        this.counter = value;
    }

    @Override
    public int getCounter() {
        return counter;
    }

    @Override
    public void copyForRespawn(CustomClass deadPlayer) {
        counter = deadPlayer.counter;
    }

}

Dispatcher

public class PlayerDispatcher implements ICapabilitySerializable<CompoundNBT> {

    @CapabilityInject(ICustomClass.class)
    public static Capability<ICustomClass> PLAYER_COUNTER;

    private ICustomClass instance = PLAYER_COUNTER.getDefaultInstance();

    @Nonnull
    @Override
    public <T> LazyOptional<T> getCapability(@Nonnull Capability<T> cap, Direction side) {
        return getCapability(cap);
    }

    @Nonnull
    @Override
    public <T> LazyOptional<T> getCapability(@Nonnull Capability<T> cap) {
        if (cap == PLAYER_COUNTER){
            return LazyOptional.of(() -> (T) instance);
        }
        return LazyOptional.empty();
	}
  
  @Override
    public CompoundNBT serializeNBT() {
  		return (CompoundNBT) PLAYER_COUNTER.getStorage().writeNBT(PLAYER_COUNTER, instance, null);
    }

    @Override
  	public void deserializeNBT(CompoundNBT nbt) {
  	PLAYER_COUNTER.getStorage().readNBT(PLAYER_COUNTER, instance, null, nbt);
    }
  
}

Storage class

public class CounterStorage implements Capability.IStorage<ICustomClass> {

    @Override
    public INBT writeNBT(Capability<ICustomClass> capability, ICustomClass instance, Direction side) {
        CompoundNBT tag = new CompoundNBT();
        tag.putInt("counter", instance.getCounter());
        return tag;
    }

    @Override
    public void readNBT(Capability<ICustomClass> capability, ICustomClass instance, Direction side, INBT nbt) {
        CompoundNBT tag = (CompoundNBT) nbt;
        instance.setCounter(tag.getInt("counter"));
    }

}

The event handler

@Mod.EventBusSubscriber
public class CapEventHandler {

    @SubscribeEvent
    public static void onTest(PlayerInteractEvent.RightClickItem event){
        PlayerEntity player = event.getEntityPlayer();
        if (event.getItemStack().getItem() == Items.GUNPOWDER){
            player.getCapability(PlayerDispatcher.PLAYER_COUNTER).ifPresent(customClass -> {
                customClass.setCounter(customClass.getCounter() + 10);
                System.out.println("Current value is: " + customClass.getCounter());
            });
        }
    }

    @SubscribeEvent
    public static void onAirRightClick(PlayerInteractEvent.RightClickEmpty event) {
        PlayerEntity player = event.getEntityPlayer();
        ItemStack item = player.getHeldItemMainhand();
        if (item.isEmpty()) {
            player.getCapability(PlayerDispatcher.PLAYER_COUNTER).ifPresent(customClass ->{
                System.out.println("Current value is " + customClass.getCounter());
            });
        }
    }

}

Another event handler

public class PlayerPropertiesEvent {

    public static PlayerPropertiesEvent instance = new PlayerPropertiesEvent();

    @SubscribeEvent
    public void onEntityConstruction(AttachCapabilitiesEvent<Entity> event) {
        if (event.getObject() instanceof PlayerEntity){
            event.addCapability(new ResourceLocation(PracticeMod.MODID, "counter"), new PlayerDispatcher());
        }
    }

    @SubscribeEvent
    public void onPlayerCloned(PlayerEvent.Clone event){
        if (event.isWasDeath()){
            LazyOptional<ICustomClass> capability = event.getOriginal().getCapability(PlayerDispatcher.PLAYER_COUNTER);
            capability.ifPresent(oldStore -> {
                event.getEntityPlayer().getCapability(PlayerDispatcher.PLAYER_COUNTER).ifPresent(newStore -> {
                    newStore.copyForRespawn((CustomClass) oldStore);
                });
            });
        }
    }
}