import QtQuick 2.15
import QtQuick.Controls 2.15

ApplicationWindow {
    width: 640
    height: 480
    visible: true

    readonly property int n: 10

    Tumbler
    {
        id: tumbler
        wrap: false
        currentIndex: n-2
        model: n
    }

    Component.onCompleted: console.log("Current index is", tumbler.currentIndex)
}

Expected output

qml: Current index is 8

Actual output

qml: Current index is 7

Problem scope

• The issue persists even if we change the value of n
• The issue does not occur if tumbler.wrap == true
• The issue does not occur if the initial value of tumbler.currentIndex != n-2
• The issue does not occur with Qt 6.2.6 and 6.4.0

Workaround
Instead of setting currentIndex declaratively, assign the desired value in the Component.onCompleted signal handler of the parent window:

Component.onCompleted: tumbler.currentIndex = n-2

This workaround must be applied to the parent window, not to the Tumbler itself.