Hi,
Thank you for the access.
I was able to find the issue.
I had to change the code:
if(isset($element->$column) && ($key===$k1 || $key===$params->table) && is_string($this->displayByType($params->types,$element,$column,$params->action['date_format'], true ))){
$square .= $this->displayByType($params->types,$element,$column,$params->action['date_format'], true);
to:
$result = $this->displayByType($params->types,$element,$column,$params->action['date_format'], true );
if(isset($element->$column) && ($key===$k1 || $key===$params->table) && (is_string($result) || is_numeric($result))){
$square .= $result;
in the file administrator/components/com_hikashop/classes/massaction.php
I'm not sure why I didn't had the problem on my end. Maybe because of a different version of PHP.
Anyways, I'll add that patch for the next version of HikaShop so you won't have to do anything when you update.