I've never made a field that didn't use the Advanced setting "Save field value" ... yet when opening a field group to edit recently, a bunch of custom fields had that box disabled, and the vale wasn't saving. Maybe these were created before that was an option...? I had to open each field (40+) and go to Advanced > Save field value.
Request/suggestion: a visual indication of non-saving fields would be very helpful. Even a toggle near where the Delete button is could make sense. I don't know if this is a known issue, but just in case it helps. Having a non-saving field is basically like "disabling" the field which shouldn't be so easy to miss. Thanks.