If a second monitor is added or removed before starting a Qt application (e.g. when a laptop is docked or undocked), QWidget::restoreGeometry() no longer restores the size of the application on startup. The behavior is reproducible with Qt 5 applications such as KeePassXC and Audacious.

I believe the culprit is this code:

    // Sanity check bailing out when large variations of screen sizes occur due to
    // high DPI scaling or different levels of DPI awareness.
    if (restoredScreenWidth) {
        const qreal factor = qreal(restoredScreenWidth) / screenWidthF;
        if (factor < 0.8 || factor > 1.25)
            return false;

Note that restoredScreenWidth is actually the total desktop width (all monitors). It does not seem like a good idea to assume that DPI has changed every time the desktop width changes, since the width can change for other reasons as well.