I am using the graphical interface to setup tabs and fields for a cpt. I am having a problem with moving a field into a group. I use the handle on the left to drag a single field into a group, the field gets moved BUT the contents of the field in this case a thumbnail vanishes, meaning all thumbnails of all cpts vanish although the id of the single image field has not changed.
If you move a top field into a group as a subfield, the subfield will not display the value of the top field because now, the group field will save value to the database under the group ID. Please read more here https://metabox.io/plugins/meta-box-group/?swcfpc=1