Hi,
Thanks for the report and sorry for the delay.
You should be able to re-download HikaShop 2.5.0 in order to get the patch.
Otherwise, you can apply it manually by editing the view "backend | your-backend-template | product | variant" and replacing
foreach($this->fields as $fieldName => $oneExtraField) {
By
$this->fieldsClass->prefix = 'variant_'.time().'_';
foreach($this->fields as $fieldName => $oneExtraField) {
Because the patch will be in the next release, you can otherwise directly edit the view file "administrator/components/com_hikashop/views/product/tmpl/variant.php" ; so you wouldn't have to remove the view next time you will update.
Regards,