Watch Face Heart Rate Null to Trigger Blank Screen

I am trying to enable non-AMOLED devices to blank the watch face screen when heart rate is not detected in low power mode for some period of time, e.g., 1 minute, in order to conserve battery. I am also using onPartialUpdate to update heart rate and seconds in low power mode for compatible devices. I got it to work in the simulator, but when I tested it on my VA3M, the screen did not blank.

First I made a function in a separate Util.mc file to determine whether the time limit has been exceeded for null heart rate:

    function getHeartRateNullExceeded() {
		var heartRate = Activity.getActivityInfo().currentHeartRate;

		if (heartRate == null) {
			
			// This doesn't blank the screen in the simulator:
			// var timeLimit = new Time.Duration(1 * 60);
			// var hrHistory = Act.getHeartRateHistory(timeLimit, true);
			// if (hrHistory == null) {
			// 	return true;
			// }
			
			// So I did this instead:
			var currentTime = new Time.Moment(Time.now().value());
			var hrTime = currentTime;
			var hrHistory = Act.getHeartRateHistory(1, true);
			var hrSample = hrHistory.next();

			if ((hrHistory != null) and (hrSample.heartRate != Act.INVALID_HR_SAMPLE)) {
				hrTime = hrSample.when;
			}

			var elapsedTime = currentTime.subtract(hrTime);
			var timeLimit = new Time.Duration(1 * 60);

			if (elapsedTime.greaterThan(timeLimit)) {
				return true;
			}
			else {
				return false;
			}
		}
		else {
			return false;
		}
	}

Then I used this function in onUpdate in View.mc:

    function onUpdate(dc) {

		// Clear clip
		if(gHasPartialUpdate) {
			dc.clearClip();
		}
				
		// Blank screen in sleep mode if HR is not detected
		if (!isAwake and gSettings.hrBlankScreen) {
			var hrNullExceeded = Util.getHeartRateNullExceeded();
			if (hrNullExceeded) {
				dc.setColor(Gfx.COLOR_BLACK, Gfx.COLOR_BLACK);
				dc.fillRectangle(0, 0, dc.getWidth(), dc.getHeight());
				blankScreen = true;
				return;
			}
		}
		
		// update screen
		blankScreen = false;
    }

And in onPartialUpdate in View.mc:

    function onPartialUpdate(dc) {

		if (gSettings.hrBlankScreen) {
			var hrNullExceeded = Util.getHeartRateNullExceeded();
			if (blankScreen) {
				return;
			}
			else if (!blankScreen and hrNullExceeded) {
				dc.clearClip();
				dc.setColor(Gfx.COLOR_BLACK, Gfx.COLOR_BLACK);
				dc.fillRectangle(0, 0, dc.getWidth(), dc.getHeight());
				blankScreen = true;
				return;
			}
		}
		
		// Draw seconds with clip

		// Draw heart rate value with another clip
    }

Note: Variables starting with "g" are global, and other non-declared variables are class wide in the View file.

To prevent onPartialUpdate from writing a new clip over an otherwise blank screen, I used the variable blankScreen true/false to tell it to wait until onUpdate refreshed the entire screen again.

In the simulator, this code successfully blanks the screen when HR is turned off in low power mode, although it is immediate. (It does not wait 1 minute.) Then if HR is turned back on or the device exits low power, the entire screen updates as intended. However, on my actual VA3M device, the screen never blanks.

Is there a different way I should be detecting null heart rate so it will work on the actual device?