Cannot see the form item for editing

I am using a three Field Group add-in modules in total including this one:

https://www.drupal.org/project/field_group_markup
https://www.drupal.org/project/popup_field_group
https://www.drupal.org/project/field_group_label

Having enabled the module...

When I go to edit a Field Group in order to add an HTML element, I cannot see the form item...

I'm left wondering whether there might be some kind of clash with either of the other plugin modules:

https://www.drupal.org/project/popup_field_group
https://www.drupal.org/project/field_group_label

...and what I should do next to investigate?

PS: Obvious candidates such as multiple cache clears already tried.