Addons form doubled in product page

Hi,
Because in your product, in the "short description" section, you manually entered another addon section (screenshot_1) and it was displayed outside (screenshot_2).
Maybe because you copied-pasted from somewhere else and accidentally dragged an addon section without knowing.
In WordPress text editors, there are usually 2 tabs: Visual and Code. Only when you click on the Code tab can you clearly see what you entered, because web browsers can let you copy a lot of things like HTML, links, media, ... not just plain text. Check the Code tab to avoid copy-pasting mistakes.
Regards!