Hello,
Yes, glad to see that you have found the cause of the problem yourself, well done.
The default template test point is to be sure that the root issue don't come from HikaShop default file, that was just a first step to know where to look the root issue.
The first idea was the template, and secondly the HikaShop override view, the point with the override system is that as we keep your custom while updating (we have to proceed like this of course).
But as you point yourself, the counterpart is that suddenly sometime make recent views and files work together with old customized view can leads to this kind of issue.
Regards