Hello,
I think there is a small issue when using UIPlayTween in combination with TweenAlpha. I have a sprite with a TweenAlpha on it which goes from 0 to 1, and I put a UIPlayTween on it which toggles the TweenAlpha and is triggered on click. The problem is that when the sprite is invisible the click trigger is no longer registered, thus the Tween doesn't play anymore, remaining completed faded out.
I checked the collider and it's just the same (at first I thought the collider got resized to match the sprite which being invisible resulted in 0 size collider but that is not the case).
I also wanted to see if there wasn't any issue with the way I set up the playtween and I put "Debug.Log('object clicked')" on the first line of the OnClick method in UIPlayTween, to see if the PlayTween gets the event but somehow doesn't trigger the TweenAlpha. However the OnClick method is not called at all when the sprite has alpha = 0.
TL;DR UIPlayTween OnClick doesn't trigger if the sprite is invisible.