Just as an FYI - Hikashop v4.1.0 just added webp as for its thumbnail generation...
https://www.hikashop.com/forum/product-category-display/897568-images-are-gone-after-update-to-4-1-0.html#307710
...so you are likely to get some traffic from people looking for why their product thumbnails are kicking out 403's.
Fortunately, the Hikashop forum is giving the right answer. Maybe this post will help others too?
The fix for broken Hikashop thumbnails is to add webp and WEBP to the list of allowed frontend and backend files extensions in admintools .htaccess maker. (see attached screenshot)