I am struggling with qtvirtualkeyboard on embedded linux device with qt 5.9.4

I created a start.qml file which looks as follows:

import QtQuick 2.9
import QtQuick.Window 2.3
import QtQuick.Controls 2.2
import QtQuick.VirtualKeyboard 2.1

ApplicationWindow {
    width: 800
    height: 1280
    flags: Qt.FramelessWindowHint
    visible: true

    Item {
        id: root
        width: 800
        height: 1280
        visible: true

        Item {
            id: appContainer
            anchors.left: parent.left
            anchors.top: parent.top
            anchors.right: parent.right
            anchors.bottom: inputPanel.top

            TextField {
                x: 10
                y: 10
                color: "#192e4c"
                maximumLength: 8
                inputMethodHints: Qt.ImhDigitsOnly | Qt.ImhHiddenText
                focus: true
                onActiveFocusChanged: {
                    if (activeFocus) {
                        Qt.inputMethod.update(Qt.ImQueryInput)
                    }
                }
            }

        }

        InputPanel {
            id: inputPanel
            y: Qt.inputMethod.visible ? parent.height - inputPanel.height : parent.height
            anchors.left: parent.left
            anchors.right: parent.right
        }
    }

}

and this works as expected - there is a keyboard with digits only and I can enter digits to the TextField.

If I modify my qml as follows and try to use my TextField in stacked qml there is a full keyboard showing on the screen and each key press generates an "input method is not set" message on the terminal. Digits are not entered into TextField.

import QtQuick 2.9
import QtQuick.Controls 2.2
import QtQuick.VirtualKeyboard 2.1

ApplicationWindow {
    width: 800
    height: 1280
    flags: Qt.FramelessWindowHint
    visible: true

    Item {
        id: root
        width: 800
        height: 1280
        visible: true

        Item {
            id: appContainer
            anchors.left: parent.left
            anchors.top: parent.top
            anchors.right: parent.right
            anchors.bottom: inputPanel.top

            StackView {
                id: stack
                anchors.left: parent.left
                anchors.top: parent.top
                anchors.right: parent.right
                anchors.bottom: parent.bottom

                initialItem: "qrc:/test.qml"
            }
        }

        InputPanel {
            id: inputPanel
            y: Qt.inputMethod.visible ? parent.height - inputPanel.height : parent.height
            anchors.left: parent.left
            anchors.right: parent.right
        }
    }

}

This is the content of test.qml pushed on stack

import QtQuick 2.9
import QtQuick.Controls 2.2

Item {
    width: 800
    height: 1280

    TextField {
        x: 10
        y: 10
        color: "#192e4c"
        maximumLength: 8
        inputMethodHints: Qt.ImhDigitsOnly | Qt.ImhHiddenText
        focus: true
        onActiveFocusChanged: {
            if (activeFocus) {
                Qt.inputMethod.update(Qt.ImQueryInput)
            }
        }
    }

}

Regards,

Michal