Multiple instances of the same field on a root form is not supported.
When a field appears in one or more formlets that are on a root form and/or the field is on the root form itself, there is potential for loss of data integrity. This risk increases each time the same field is shown to end-users on the same form.
You can only explicitly add a field to the base root form or formlet once. Once added, the field is disabled in the Fields pane on the left. A field can appear multiple times on a form overall if one or more formlets embedded on the root form have the same field; however this is not recommended.
For example, if the root form 'Contact Information' has the 'Name' field on it and the formlet contains the same field, then 'Name' can appear on the form twice.
The latest input to that field will persist across the entire form for any editable instances of the field.
For example, if the user updates the 'Name' field on the formlet, then 'Name' will also update in the root form since the most recent value will persist across the entire form.
The only way to prevent any change in value to a specific field is if every instance of the field is read-only. If one or more instances are editable on the form, then the most recent value will persist across the read-only instances of the field.
Before publishing, review how your formlets interact with your form. Ask yourself if you could remove a field from the root form because your formlets cover the various use cases for the form.
