QMessagebox not responding IOS 11

QMessageBox does not close (i.e. it is like if the buttons are inactive) when running on iOS 11.3. The same application running on iOS 9 or 10 works normally. The problem occurs with the static methods or with the creation of a QMessageBox followed by exec().

QMessageBox::StandardButton reply = MSGBOX_CLASS::information (this, "test", "test", QMessageBox::Ok | QMessageBox::Cancel); 

I found a workaround:

All these QMessageBox are always triggered through QActions, either from a QToolBar or a QMenuBar or a QMenu. If I connect these actions to their slots using Qt::QueuedConnection the problem is solved. The QActions and their slots are in the same thread.