Imho, the rectangle animation is better, but the spinner is more typical. I agree it should be made consistent. If the 2 animations represent something different from each other, that should be clarified. Else, maybe both could always run simultaneously, like on the app's opening update.

I would suggest showing the rectangle shimmer for the first time when no data is available. However, after the data has been loaded once, for refreshing purposes, you can switch to displaying a rounded progress bar.