PS 8.1.7, Incorrect 'free shipping' carriers/rates

[FuzzySlug]

Hello,
There are many variables to this problem so I'm just putting the details out there to see if anyone else is having a similar issue, or if anyone has any troubleshooting tips.

We are currently using PrestaShop 8.1.7, hosted on Linux with Apache.
We utilize PrestaShop carriers, along with a 3rd party module "UPS Shipping" by Webkul in order to get live UPS rates.

Ever since we upgraded from 1.7.8.7 to 8.1.7 (which is also when we installed the UPS Shipping module) we have been getting orders where customers are selecting free shipping rates that should not be free. The frequency of these 'free shipping' orders is about 1-2 every few days. This is not only happening to carrier options from the UPS Shipping module, but through our built-in PrestaShop carriers as well.

For example, if we have PrestaShop Carrier "XYZ" that states "Total weight" 0 - 6 lbs has a cost of $20.00, most orders will abide by this; however, every few days we will receive an order that has gotten this Carrier for Free. We have analyzed these orders extensively and cannot see any obvious correlations. The customers do not have any discounts/coupons for "Free Shipping" or anything that stands out as to why they received this carrier for free either.

We are convinced that customers are seeing the rates as "Free" (as opposed to seeing a valid rate, but not being charged for it when clicking "Place Order") because we have customers that are selecting carriers such as "UPS Next Day Air" which is normally an extremely expensive rate.

Unfortunately since we have not been able to correlate these occurrences we also have not been able to replicate the issue ourselves.

We understand that there could possibly be a conflict between PrestaShop and the 3rd party module by Webkul; however, we have not seen any other posts that speak about this issue, and it isn't clear to us how the module would override and return a free carrier rate for PrestaShop carriers such as the "XYZ" example.

Edited October 15 by FuzzySlug (see edit history)

[ComGrafPL]

Have you tried to duplicate those orders and what what may cause it? Maybe zone, customer groups or any other filters are on?

[FuzzySlug]

10 minutes ago, ComGrafPL said:

Have you tried to duplicate those orders and what what may cause it?

We have made multiple attempts to replicate the issue however all have been unsuccessful. This issue spans multiple customer groups and zones so it does not appear to us that any particular group or zone is causing this to occur. We've had this issue occur with brand new customer accounts as well as accounts that were created several years ago too.

[yama]

14 hours ago, FuzzySlug said:

We understand that there could possibly be a conflict between PrestaShop and the 3rd party module by Webkul

High probability, especially with them.

They probably know the problem but they are waiting your request for a fix to access your BO instead than fix to everyone.