Yes, I am aware that Guest isn't an option in the free version. If you need a copy of Hika I can send it over.
Sorry, but no for the Menu Item possibility.
This is the checkout process for a new user. (Login/Register/Guest) It has nothing to do with a menu item being set to HikaShop's registration (which has been setup that way for a few years already).
https://shepardmoon.com/login works as expected.
The only thing we changed was to enable the Guest option in Hika. Oddly, the header changes from Register to Guest and the button at the bottom changes from Register to Next. It's the the text block inputs do not change.
It seems there is some sort of conflict with Helix preventing the Guest option from switching.
Error Reporting shows:
Warning: A non-numeric value encountered in /home/phillipsm/public_html/plugins/system/helix/core/helix.php on line 548
Browser Console on that page shows an issue with the modernizr js in the Helix plugin
Again, if I change the default template to Protostar it works as expected.