Hi,
I'm bumping this as I've just spent around 5 hours trying to figure this out. Hopefully this may help someone.
The answer for me was to simply recreate your Flow. For whatever reason, PowerApps doesn't play nice if your Flow is created before the PowerApp (?). I got to the stage of creating my Timer within the PowerApp (OnTimerEnd Runs the Flow and adds the response to a collection), deleted the existing Flow, recreated it manually, added the new Flow to OnTimerEnd from the Flow button in the command bar within the Action tab (I believe this is required to refresh the Flows available to you in the PowerApp), and built my ClearCollect function around it e.g. ClearCollect(Weather, WeatherFlow.Run("London")).
Gave that a test and it all worked, I now have data in my table not the boolean value of "True".