Hi,
This usually indicates an issue with the customization of the product page layout.
If you look at the HTML of the page with your browser's developer tools, you'll see this:
monosnap.com/file/Lg7ufJOiBh2nX5GnaT4Maqr3IXGUXV
The price, add to cart etc area has been included inside the contact button area.
Hence when the contact area is refreshed with the one from the new variant, it doesn't contain these elements and thus you don't see them anymore.
This usually means that you're missing some </div> somewhere in the "show_default" or "show_tabular" view override (depending on the layout you're using).