Hi,
The issue comes from how your product page layout has been customize by you, your web designer or your template provider.
The price area has been moved inside the quantity input/add to cart area:
monosnap.com/file/tJp54B2yaq6BJwe2aI4jxHYjPKnixU
Because of that, when you change the characteristic selection and the system refreshes the different areas of the page with the information of the current variant, it refreshes the quantity area with data for the quantity area of the selected variant and it doesn't contain the price information and thus you loose the main price area.
So you'll have to see with your template provider or the person who customized the product page so that they can fix that and move the main price area outside of the quantity main area. It will then work properly.