onPartialUpdate not called even though device supports partial updates?

I'm developing a watch face for Forerunner 245. The device supports partial updates (`Toybox.WatchUi.WatchFace has :onPartialUpdate` is true). The method implementation has the same signature shown in the documentation (https://developer.garmin.com/connect-iq/api-docs/Toybox/WatchUi/WatchFace.html#onPartialUpdate-instance_function). The documentation says printing can be used in similartor, but either my `onPartialUpdate` method is never called, or the documentation is wrong and printing is not working in the simulator.

My partial update method is just:

function onPartialUpdate(dc) { Sys.println("Partial update"); View.onPartialUpdate(dc); }

Any thoughts on what I may be missing?

Min API level in my manifest file is 3.3.0. App type is watchface.