If you’re trying to get this to the developer then you need to open a new support ticket. https://support.advancedcustomfields.com/new-ticket/.
All of these type of fields, like you say, use select2. I don’t know if you can tell select2 to load all the fields ahead of time or not, I don’t know all that much about select2. If you can it would be done though adding a filter in javascript for the select2_init action documented on this page https://www.advancedcustomfields.com/resources/adding-custom-javascript-fields/.
