Not sure if it’s 5.2 specific problem but when you have a game object with Event Trigger component and Buttons added as its children game objects, the way buttons are clicked is altered.
Normally, you can still move your mouse a bit while clicking to successfully click a button but if a button’s parent has event trigger component, you no longer have this “margin” thus lowering usability of UIs.
I have reproduced and confirmed this bug in a new project. I hope it gets fixed