Just now I was facing the same issue, but I'm not loading any image, I'm taking snapshots of Nodes. So, I wanted to expand on the @jewelsea answer with my workaround specifically for this use case:

// Get the screen on which the node is displayed
public Screen getScreenFor(Node node) {
    Bounds bounds = node.localToScreen(node.getLayoutBounds());
    Rectangle2D toRect = new Rectangle2D(bounds.getMinX(), bounds.getMinY(), bounds.getWidth(), bounds.getHeight());
    return Screen.getScreens().stream()
        .filter(screen -> screen.getBounds().contains(toRect))
        .findFirst()
        .orElse(null);
}

// Node that w and h can be retrieved directly from Node, but I needed them because they may not match in my case
public WriteableImage snapshot(Node node, double w, double h, SnapshotParameters parameters) {
    Screen screen = getScreenFor(node);
    // Use this workaround only for HiDPI screens
    if (screen.getOutputScaleX() != 1.0) {
        double scale = screen.getOutputScaleX();
        int scaledW = (int) (w * scale);
        int scaledH = (int) (h * scale);
        WriteableImage snapshot = new WriteableImage(scaledW, scaledH);
        parameters.setTransform(Transform.scale(scale, scale));
        node.snapshot(parameters, snapshot);
        return snapshot;
    }
    return node.snapshot(parameters, null);
}

Edit: just a little rant, I'm quite tired of dwelling with JavaFX bs! Hope this could save someone a headache