Hello Paolo,
Thank you for your quick reply.
I have tried desactivating all plugins, but it didn’t change anything. However I finally identified where it may come from:
When I click on the “Fill user details” in the billing details panel, the payment page loads very quickly. If I don’t click and write whatever myself, the payment page loads very slowly.
It may be related to these user informations? Does it make sense to you?
I guess the solution will be to click this button ??