I got same error with "forceActiveFocus". I don't found a correct way to update event on virtual keyboard.
Some testing component in source.
https://code.woboq.org/qt5/qtdeclarative/tests/auto/quick/qquicktextinput/tst_qquicktextinput.cpp.html#_ZN19tst_qquicktextinput15signal_acceptedEv

I changed the textfield to textarea and a new manual enter button solved the problem temporarily.
At this time, text area goes over botttom of screen while i'm typing newline. This crashed too. :D

@ekkescorner i tried this one, too. But TextField signal onAccepted automatically hides the keyboard. Nothing happened with Keys.onReturnPressed. I need modify the onAccepted method on TextField. I found this in qt source, https://code.woboq.org/qt5/qtbase/src/gui/kernel/qinputmethod.cpp.html#214

/*
    Requests virtual keyboard to close.
    Normally applications should not need to call this function,
    keyboard should automatically close when the text editor loses
    focus,((And if someone press enter)) for example when the parent view is closed.
*/
void QInputMethod::hide()
{
    Q_D(QInputMethod);
    QPlatformInputContext *ic = d->platformInputContext();
    if (ic)
        ic->hideInputPanel();
}

Here's an idea: detect the enter key (you do it in onAccepted if I understand you well. An alternative is to use Keys.onPressed), and in the slot switch focus to some off-screen control. Or, for that matter, switch it back to your current input. The keyboard should stay up this way.