Tabledrag is resetting the region value if items are nested

Problem

This issue is linked with the fieldgroup issue at https://www.drupal.org/project/field_group/issues/3085858 🐛 Drag and drop acts weird, sometimes not resetting the parent, or even clearing the region value Needs review
When you are dragging a group or field that is in the content region to a new place as root element, there is no issue. The issue occurs when you drag the group or field to become a child of a group. If you click on the 'show row weights' button, you will see that the region value is lost.

Before dragging:

After dragging:

Solution

The issue seems to be related with 'field-name' that is set as source for the region. Which is not correct. Simply removing the configuration fixes the issue. Dragging the field in another region also keeps working.