Syncing Changes Loading Explained
The real power of ACF’s local JSON feature is the ability to sync changes. This allows multiple devs to work on a project, use git to push/pull files, and keep all databases synchronized with the latest field groups, post types, taxonomies, and options pages.
Items stored in JSON will be available for sync when either the items do not exist in the database, or when the JSON version contains a higher “modified” value (within the JSON array) than the post modified date recorded in the database.
When items are detected for synchronization, you will see a new tab above the list table where you can select the items to be imported.