1062 Duplicate entry 'XYWZ' for key 'group_key' only in control panel

-- HikaShop version -- : 3.4.1
-- Joomla version -- : 3.9.10
-- PHP version -- : 5.6.6
-- Error-message(debug-mod must be tuned on) -- : 1062 Duplicate entry 'XYWZ' for key 'group_key'

Hi,
I know I have an old php and hikashop version but I'm still waiting to update php on my hosting to update all. With this configuration, it works everything's well for 1 year until some days ago. All hikashop works perfectly only in the control panel appear this error: 1062 Duplicate entry 'XYWZ' for key 'group_key' the number XYWZ change at any login. I search this value in all DB but without a result.
How can i resolve the problem ?

Many thanks and best regards.

Luca

Hi Nicolas,
the trick of modify /libraries/joomla/database/exception/executing.php to print the query is very useful, trying this the query is:

SELECT *, SUM( case when o.order_currency_id = '1' then o.order_full_price end ) AS Total, COUNT(o.order_id) AS order_number FROM k4x6e_hikashop_order as o LEFT JOIN k4x6e_hikashop_user as a ON o.order_user_id=a.user_id LEFT JOIN k4x6e_users as u ON u.id=a.user_cms_id LEFT JOIN k4x6e_users AS b ON a.user_cms_id=b.id WHERE a.user_partner_activated=0 AND o.order_status IN ('shipped') AND a.user_id IS NOT NULL AND o.order_type='sale' GROUP BY a.user_id ORDER BY Total DESC LIMIT 10