Hi,
Well, normally, you're supposed to have one extra variant for the - and - choice which is the default one.
I don't know why the other works and not this one but that's the only thing I can see which is not normal on your screenshots.
I would recommend to follow that procedure for the product with the problem:
1. Delete all the variants of the product on the listing of variants that you can access via the button "manage variants" on the product edition screen.
2. Delete the characteristics of the product.
3. Save the product.
4. Add the characteristics again.
5. The system will regenerate all the variants automatically and you should be able to see the dropdowns properly on the front end.
That should help fix the issue. Then, delete the variants you don't want and configure the price of each variant like you need.