Hi Jerome
I have managed to track this down a bit further. It is not the template that is causing an issue but there appears to be a conflict with MaxiMenu CK.
As soon as the product edit page loads the following error appears in the console:
TypeError: this._addClass is not a function[Learn More] jquery-ui.min.js:14:30077
_create https://..domain.tld../media/com_hikashop/js/jquery-ui.min.js:14:30077
It only seems to happen when the product edit page is opened from the vendor control panel, it is not there on the back-end product edit page.
Is this a JQuery conflict perhaps!
Best regards
Trevor