Hi,
Thank you for the access.
I found out that the issue was related to another change we made to be able to support discounts made directly on variants. For this, we have to add the discount on the price of the variant. However, at the point where this is done, the price of the variant is, in your case, a copy of the price from the main product. And that price from the main product already has the discount on the main product applied to it.
I've modified the code so that when the system tries to add a discount to a price, it first checks if the price doesn't already have a discount applied. If so, it skips the process.
I've tested the modification on your website and I can confirm it fixes the problem.
For anyone with the same issue, download again the install package of HikaShop on our website and install it on yours and it will add the patch.