Wrong amount and shipping cost not showed (PS1.7.4.2)

[DARKF3D3]

Hello, I'm writing this post because It's months since I discovered a bug into my shop but I can't find a solution to it.

Into some orders received the shipping cost it's not showed.

The customer when placing the order see everything correctly and the payment it's completed with the correct amount.

But then into back office I see the order without the shipping cost and an alert into payment block that say that customer has paid the wrong amount:

Here you can see the total amount for the order and shipping cost of 0€ (the shipping costo should be 5,90€):

To correct the amount on these orders, I created a product with a cost of 5,90€.

The strangest thing happen now, in fact if I add this product to fix the price, then the shipping cost it's added again.

So since I also added the same amount with the product, so instead of being lower than € 5.90, the total amount become higher than 5,90€.

And the only way to fix again this it's to add a free shipping discount code.

 

This happens on 5 of the orders but I can't, not only on a single payment method.

There's anyone who had a similar issue?

Edited January 8, 2020 by DARKF3D3 (see edit history)

[DARKF3D3]

No one encountered this problem?