Hi,
You have a SEF problem which is really wired.
Can you please create a menu for your checkout and use the option "force menu on checkout" to this menu ?
At this moment, all links for the checkout will use the same menu (the same entry point) and I guess (and I hope too) that creating a menu will help Joomla and the SEF system to find correctly the views.
Do you use the default joomla SEF system or are you using a special extension ?
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.