Product Image Disappears

That is strange, sounds like possibly a JS conflict, can you link me to your site? Are you running the latest versions of Woocommerce/Woo Radio Buttons/Wordpress? Lastly I would try activating the default theme to see if it fixes itself, if so your problem is in a theme file somewhere. If not then try deactivating your plugins and activate them one at a time until you find the conflicting plugin.

I tried this plugin and after activated products with an alternate image for a variation showed it for both options. Note an explicit variation images was only set for one, not both, but it displayed for all.