What are dual camera limitations?

In some cases when I use "builtInDualCamera" capture device I get white blank depth photo. In other cases it works fine.

So I guess there is a limitation. I use this code to get depth image:

private func saveDepth(name: String, photo: AVCapturePhoto) throws -> URL {
    guard var depthData = photo.depthData else {
        throw CameraError.photo("No depth data")
    }

    print("DEBUG: depth data quality \(depthData.depthDataQuality)")

    if let orientationValue = photo.metadata[kCGImagePropertyOrientation as String] as? UInt32 {
        if let orientation = CGImagePropertyOrientation(rawValue: orientationValue) {
            depthData = depthData.applyingExifOrientation(orientation)
        }
    }

    let converted = depthData.converting(toDepthDataType: kCVPixelFormatType_DepthFloat32)
    let image = CIImage(cvPixelBuffer: converted.depthDataMap)

    guard let colorSpace = image.colorSpace else {
        throw CameraError.photo("Can not get image color space")
    }

    guard let data = context.tiffRepresentation(
        of: image,
        format: .Lf,
        colorSpace: colorSpace,
        options: [:]
    ) else {
        throw CameraError.photo("Can not create TIFF")
    }

    let url = Path.cachePath.appendingPathComponent(name + "_depth.tiff")
    try data.write(to: url)

    return url
}

Any information about maximum distance or some other limitations for dual camera?