QQC2.ComboBox is typically implemented as a contentItem: T.TextField with a binding like readOnly: !control.editable. The said TextField apparently never looses focus unless the combobox's popup is opened, so onFocusChanged does not get called when simply switching the focus to another control.

As a consequence, it prevents, for example, repositioning a context menu toolbar whenever the text field is refocused.

See also: QTBUG-125628

Reproducible example in the attached file: click on the ComboBox, then on the button below, then on the ComboBox again; try clicking on the indicator to open the popup and see the difference in logs.