Hi,
I think that your problems comes from view overrides.
Can you switch temporarily to the default template of Joomla on your frontend, and try again with the default template ?
It should definitely help with seeing the delete icons. If so, it means that the issue comes from a file in the templates/YOUR_TEMPLATE/html/com_hikashop folder. Probably in the "upload" subfolder there.
So try renaming the upload subfolder to something else via FTP in order to deactivate the overrides inside it.
Also, on your link I was able to select several images and all of them were added. I was also able to select several images several times with the upload icon or drag & drop.