Hi Again Nicolas,
I think I identified what causes the /step-1
If I add a product to the cart, proceed to checkout and just submit it. It goes just fine and displays the thanks you message.
BUT, if I adde the product, proceed to checkout, uncheck the 'Use the same address as for billing', select another address and try to submit. Then I get redirected to the top, the step-1 is added to the url and I have to press the finish button again.
Would you mind following this steps and see if you get the same problem?
Thanks