Widget blueprint variable lose its reference

If I add a debug in the Construct Event on my widget blueprint, it’s indeed called several during the play.
I use my widget component as a billboard, and during the tick event I scale it, rotating it, and update its position over the unit, but it’s never destroyed.
I have try to change the space to render from World to screen, but that doesn’t change anything.

Am I missing something ? Or is there a better way to draw a GUI overlay on the top of my unit like RTS game ?