Hello everybody, It’s been a short that I use UE4, and I have a problem with my shadows. At the beginnings, when a clicked on the “builds” button, shadows were perfect, and details. But 1 a click on this button, My shadow was made by strange shape. I want to get the previous good shadows back, can you help me? Thank you 
Hi
What quality are you previewing in and what is you LOD?
Hello Dumbo1999 -
Take a look at our Lighting Troubleshooting Guide found here:
A new, community-hosted Unreal Engine Wiki - Announcements - Epic Developer Community Forums
If as it looks above that you are using Static Lighting, specifically the section on Lightmaps and Shadow Quality as well as the section on setting Production versus Preview Level Light Builds.
Thank You