Hello,
This software seems like it should still be in beta
HikaShop 3.0.0 and HikaAuction 2.0.0 came out at the same time and both were heavy versions so we fixed every issue that we were having on our end and that customers were reporting, but we didn't had a lot of customers who tested the HikaAuction "Use Hikashop Checkout" option.
So if you found an issue, we will be more than glad to quickly fix it.
We just succeed to reproduce that issue on our end so we'll fix it as fast as possible.
We apologize for any inconvenience this may have caused.
EDIT
Also, note that this issue is only appearing with the new "Use Hikashop Checkout" feature which wasn't tested by a lot of customers, so for the moment the solution can be to disable it via "HikaAuction->Configuration" and use HikaAuction like it's explained on that tutorial :
www.hikashop.com/support/documentation/3...r-first-auction.html