Hello,
we've been having the same problem: sometimes the customer pays full amount even though a voucher or discount is applied. This happens on about 5-10% of orders.
In our case we're running PrestaShop 1.7.6.7 and we've tried two distinct Stripe plugins, both the official one (202ecommerce v2.3.1) and a third party one (Stripe Payment Pro 4.1.5).
The issue seems to happen with both native discounts and discounts or vouchers created by plugins, e.g. idnovate Promotions and discounts v2.1.37
Since it happens with different Stripe plugins, I'm starting to think it's a PrestaShop problem...
Has anyone managed to fix this issue or investigate a little more?