Hello,
Yes, it looks like you had some old data in your database which were not migrated correctly.
I will add a patch in the next release which should be very similar to your own patch you sent via the "contact us" form.
Indeed, we need to make sure that the "vendor_params" is decoded or reset it to an empty object if an error occurred.
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.