Just had a weird issue with ACF PRO 5.1.8. I have a field as type of Radio Button. I have some choices set. If I click duplicate, to duplicate the group, it works, but the choices are all empty on the newly created copy. Not sure if this happens with other field types, but seems like a definite bug in this case.
Thanks for the bug report.
This should be fixed in the latest version 🙂