Steps to repro:

1. download the attached project
2. Make sure you can build a player (windowsstandalone)
3. Hit play in the gameview and click and hover the label ( some logs will appear and clicks events are listed)
4. now build a player and once its built, do the same

Result: 

Events are not registered by clicking on the label.

!label.gif!

Workarounds:
- Adding a script with an empty OnGUI method seems to fixes the problem.
- Adding a standaloneinputmethod as a compoent on the UI Document fixes the problem.

Notes (From Benoit):

I'm pretty sure the problem comes from some optimization in our Build code that detects there's no GUI active in the game, and seeing that the new Input is also present (because you have "Both" selected) it probably discards the old input events. On the other hand UIToolkit detects that the old input also available and it tries to consume the GUI events, which aren't there.