Hi,
It's precisely because you didn't loose your existing layouts (view files) that you got that issue.
You've modified the product page layout and thus HikaShop is still using that layout after the update, however, you didn't edit the CSS in the "frontend CSS file" setting of the HikaShop configuration and thus HikaShop updated it to the latest version.
However, The CSS that was present before in that CSS file to control the positioning of the elements on your version of the layout of the product page is not there anymore and has been changed to new CSS for the new HTML of the product layout page.
The best would be to remove your override of the "show_default" view file and then add back your changes to the new version of the view file via the menu Display>Views.
As a quick fix, you can also add such CSS on your website:
.hikashop_product_left_part, .hikashop_product_right_part{
float: left;
width: 50%;
}
But I would recommend the first solution so that your page layout is responsive (mobile devices).