Hello,
It sounds like you're having an issue with the additional shipping cost being charged even though it's disabled for the 3rd and 4th pallet delivery options. This may be caused by a configuration error in your shipping options or a bug in your PrestaShop version.
Here are a few things you can check to help resolve the issue:
Check the weight ranges of your shipping options to make sure they're set up correctly. Make sure that the weight range for the 3rd and 4th pallet delivery options is higher than the weight of the items you're adding to the cart.
Make sure that the "Additional Shipping Cost" option is unchecked for the 3rd and 4th pallet delivery options. You can do this by editing the carrier in the "Shipping" section of your PrestaShop back office.
Check for any overrides or customizations in your theme or modules that may be affecting the shipping cost calculation.
Try upgrading your PrestaShop version to the latest available release to see if the issue has been fixed.
If none of the above suggestions resolve the issue, you may need to reach out to PrestaShop support or a developer for further assistance.