Hello,
What "account" did you have to saved ?
I would need to understand how your vendor structure is made ; if you have subscription or something which can interact with HikaMarket and would explain why you need to save the "account" to restore the display of the vendor page.
If you need to perform that action, it means that something else happened and result of that blank page.
Unfortunately, it is not a known issue so HikaMarket 3.0 would not have a fix for that.
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.