I realized this as well, and it turns out there is a conflict between the latest version of ACF (5.3.5) and the latest version of the WPML plugin from Sitepress (3.3.6). Downgrading the WPML plugin to a previous version seemed to fix the problem.
Thanks for looking into this.
Welcome to the Advanced Custom Fields community forum.
Browse through ideas, snippets of code, questions and answers between fellow ACF users