I have been developing with this plugin for over 4 years, and other than that obnoxious redesign ya'll did a few years ago, I have only ever had one issue with it. When adding a new field on the Edit Field Group pages, if there is a long list of fields that I have already created and I need a new one, the "Add Field" button creates the new field at the bottom of the fields list. Not an issue normally, but when a client wants a new section added to a page that is already built, I have to create the new field and then drag the dumb thing back up to the top of the list. Every time. It get's very obnoxious, and I think you should build in a way to add a new field group directly beneath an existing one.