I check on http://answers.unrealengine.com/ and found someone with the same issue. I post a message in order to said that it’s not solved. But thankfully someone posted the command to deactivated the motion blur and as Nawrot said it’s working.
And with also have other problems with UMG. We were trying to put a material on an image inside a canvas but in game its scale is changing or it doesn’t appear (while it’s working in the UMG editor). And this change of scale is link to the position of the mouse 
The right image below appears only when my mouse is on the “Stop” button of UE.
