Fixed amount cart rule is duplicated after order splitting

[MHostinato]

Prerequisites

• I understand and accept the project's code of conduct.
• I have already searched in existing issues and found no previous report of this bug.

Describe the bug and add attachments

When the customer adds a fixed amount cart rule to his cart, and order splitting happens (when two different products are shipped only by different carriers), the cart rule is applied to both orders.

Expected behavior

Apply the cart only only to one of the orders (first one preferably).
But maybe the order splitting feature may be revisited completely.

Steps to reproduce

1. create two carriers in backoffice
2. create to products in backoffice
3. associate the first carrier to the first product, then associate the second carrier to the second product:
   
   
4. create a fixed amount cart rule:
   
5. add the products to the cart in frontoffice, and then add the cart rule, see the calculations are correct:
   
6. finalise the checkout process and validate the order
7. see the cart is splitted and the cart rule has been duplicated on both orders:
   
   

PrestaShop version(s) where the bug happened

8.1.1

PHP version(s) where the bug happened

8.1

If your bug is related to a module, specify its name and its version

No response

Your company or customer's name goes here (if applicable).

Hostinato

[MHostinato]

Related epic bug thread: #15491

[AureRita]

Hi @MHostinato ,

Thank you for your report, I reproduce the issue with PrestaShop version 8.1.x, as you can see :

recording.209.webm

Thank you for this clear issue ! I'll add this to the backlog so it can be fixed.

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