Problem on setting nbt tag on Item

Hello,

I dont really understand why the nbt tag in the code below is not attached to the item.

@Override
    public InteractionResult interactLivingEntity(ItemStack pStack, Player pPlayer, LivingEntity pInteractionTarget, InteractionHand pUsedHand) {
        if (pPlayer.getLevel().isClientSide()) {
            if (pInteractionTarget instanceof Mob mob) {
                System.out.println("ITEMSTACK " + pStack);
                CompoundTag nbtTag = null;
                System.out.println("nbt tag " + nbtTag);
                if (!(pStack.hasTag())) {
                    nbtTag = new CompoundTag();
                    CompoundTag nbtMobTag = new CompoundTag();

                    mob.save(nbtMobTag);
                    nbtTag.put("mob", nbtMobTag);
                    System.out.println("IN NBT NULL " + nbtTag);
                    pStack.setTag(nbtTag);
                    System.out.println("AFTER TAG SET " + pStack.hasTag());
                    pPlayer.sendMessage(new TextComponent("Shard used on " + mob.getDisplayName().getString()), pPlayer.getUUID());
                } else {
                    nbtTag = pStack.getTag();
                    System.out.println("item has tag");
                    System.out.println(nbtTag.contains("mob"));
                }
            }
        }
        return InteractionResult.PASS;
    }

    @Override
    public void appendHoverText(ItemStack pStack, @Nullable Level pLevel, List<Component> pTooltipComponents, TooltipFlag pIsAdvanced) {
        CompoundTag nbtTag = pStack.getTag();
        if (nbtTag != null) {
            if (nbtTag.contains("mob")) {
                Mob targetMob = null;
                targetMob.deserializeNBT(nbtTag.getCompound("mob"));
                pTooltipComponents.add(new TextComponent("Mob : " + targetMob.getDisplayName().getString()));
            }
        }
    }

Everytime I right click with the Item on a LivingEntity, It goes on the if(!pStack.hasTag()), but It shouldn't because we set the tag on the first right click on an Entity

Do you have a solution ?