Sadly, we still face the same issues. And I have no idea why the session coockies would be deleted. I don’t think that customers are clearing coockies themselves or are using private browser sessions during payments. I would expect that for 1 or 2 % of the payments, but not for more than 70% of the payments.
Any other ideas? The wp instance is a scratch installation without any extra plugins. It uses currently only the stripe plugins and the post-smtp plugin. It runs the latest version of wordpress and pho 7.4. (Tried php 8 as well, but same problem)