Steps to reproduce the issue

implement subform which includes a modal form
add a filed type which uses the modal, media or user field like

<field
 name="test"
 type="subform"
 multiple="true"
 >
  <form>
     <field
          name="text"
          type="user"
      />
  </form>
</field>

Click add subform and check if all modals open

Expected result

Every modal field should open

Actual result

Only first modal field opens

System information (as much as possible)

PHP Version | 7.3.14
Joomla! 4.0.0-beta1-dev Development [ Mañana ] 17-October-2019 20:21 GMT
Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:75.0) Gecko/20100101 Firefox/75.0