When opening a Subform with a SmartForm event, some of the rules of the opened Form are not executed during runtime.
During a client meeting the "When Add Toolbar Button is Clicked" rule was verified that opens the subform. It was found that two Actions were configured: "then navigate to [FormName] Form" and "then open [FormName] as a subform" referencing the same [FormName]
The "then navigate to [FormName] Form" action was disabled in the rule and the changes save. When testing the form again as per the client solution, the opened Form performed as expected.