Cannot Add Subform to Form Section

Cannot Add Subform to Form Section

It appears that we are now unable to add a new subform to the main "Section" of my existing forms - it needs to be below the main section.  This is a new situation - we have many forms with subforms inside the main section, and we can add other components to the main section, but not subforms.

Has anyone else seen this behavior?  Is there a way to allow this?  It is required for us to be able to add subforms wherever on a form we need.