UnknownPerformanceLevel is the value of IDevicePerformanceControl.GpuLevel, PerformanceMetrics.CurrentGpuLevel, IDevicePerformanceControl.CpuLevel, and PerformanceMetrics.CurrentCpuLevel if the current performance level is unknown. This can happen when AdaptivePerformance is not supported or when the device is in throttling state (see WarningLevel.Throttling).