Create Qt Quick Controls Application and alter the MainForm.ui.qml so that it contains a RowLayout which contains a TextField and then a Group Box under the TextField. Example found in MainForm_WORKING.ui.qml.

Change the anchors so that the TextField and the Groupbox has one common anchor, i.e. anchors.bottom for textField and anchors.top for the Group Box. This works as long as the margins for these anchors are the same. If the value for anchors.topmargin for the goupbox is less than anchors.bottom for the textfield, Qt Creator will hang in a couple of seconds, though not instantly.

An example which does not work (hangs Creator) can be found in MainForm_NOTWORKING.ui.qml.