No, we are not using multi-step checkout.
We make it look like that with our Cart (step 1), Checkout (step 2), and Order complete (step 3), but those are just the regular WooCommerce pages.
This is just the standard invoice link that customers click in an email, which then we require them to login to purchase and it’s here that your plugin fails. It’s a WooCommerce compatibility issue.
Could you try and see if you can recreate this issue on your end? Then let us know if you have a fix for this?