So, I noticed this topic, and I wanted to let you and possibly some viewers know about my experience with GuiObject:TweenPosition, by giving some additional details about this issue.
First create a new UIPageLayout. Open the dropdown menu of “EasingStyle”. Those are all the easing styles that appear to work with TweenPosition, but the enum lists all of them. Exponential is not one of them. Even though they are in the same enum, they aren’t all supported. Exponential, for example, will default back to the “Constant” EasingStyle if the one you requested does not exist. You will need to use TweenService if you wish to use Exponential or any of the other EasingStyles not listed in TweenSize or TweenPosition.
I wouldn’t say this is really a bug, more of a lack of features in my opinion. I realized this a couple of months ago.