The same for
Android 7.0 (Samsung Galaxy J3 2017) : Windy app, Chrome, Firefox (and Samsung Internet).
Note: When I click on a different Forecast model, the bar slider moves a little bit, but the value of the altitude stays the same.
Note 2: On Android - the Windy app & all browsers do remember the set-up altitude for 'Wind, Temperature, Dew Point and Humidity' (and also those other layers for which it should not remember & show).