Hello,
I was not able to reproduce your issue in my tests websites but I might have an idea of the source for that issue.
In the HikaMarket vendor class (administrator/components/com_hikamarket/classes/vendor.php) please replace
$vendor_access = implode(',', $accesses) . ',' . $vendor_access;
By
$vendor_access = implode(',', $accesses) . ',' . trim($vendor_access, ',');
If the problem persists, we will need more details about a value in your database for that vendor, the content of the column "vendor_access".
Regards,