An immediate fix is to set Universal Button to “Custom URL”: /wp-content/plugins/add-to-any/favicon.png
The 2x universal icon issue your site is experiencing is from a core AddToAny release that makes some important icon changes for developers. The changes can affect some sites that use a combination of your selected icon and empty text for that selected icon. This will be resolved in a future plugin release, but the fix above is most ideal anyway.
Tip for your custom icons: There is a new AddToAny advanced option called “Use custom icons.” I recommend switching to this new option so plugin updates will not overwrite your custom icons. 🙂