Using the horizontal mode in Repeatable Field Groups breaks the Fields Group editing interface.

Symptoms

When you are adding Repeatable Field Groups to a post, you have the choice to display all Repeatable Field Groups either in a horizontal or vertical layout. If you select the horizontal layout, you will not be able to add fields, and when editing existing fields, the user interface will look broken.

Workaround

Current workaround is to simply use the vertical layout – this is a global setting that changes for all posts once you save it for any post:

1. Edit a post and change the Repeatable Field Group to be displayed vertically.
2. Save the post.
3. The issue will be resolved on all posts that use this particular Repeatable Field Group.