Hello,
We have received your references and where able to see your issue on your website, but we weren't able to reproduce it on our website.
Plus, unfortunately we haven't the full access of your backend, in details we can't reach the main configuration of HikaShop, please adjust the provided backend access in order to have the full access.
Other point, it's really a shame that you have remove the default template (ProtoStar), suddenly you deprive yourself of being able to test with a default template, I mean, because maybe your issue come from your template ?... Restore a default template please.
Other theory, you have some override view in Display => Views, and checkout view group.
=> Try to save on your side all your override views, remove its from your website, and process some tests again.
If that didn't change anything you can restore your overrides view.
We are awaiting your returns to be able to progress on your subject.
Regards