Hi, I have problem with shadows in UE4.
During the preview, all the shadows are visible, but after building all shadows disappear…
Unreal runs on Epics quality.
I put my assets on the default scene (incuding default fog/sky sphere setings).
Looks like the floor mesh’s lightmap resolution is too small. Increase it to 256 or 512 and build again then see if it fixes.
Hi risne,
Jacky is correct that you need to adjust the lightmap resolution of the floor.
The “preview” shadows that you see before the light build are dynamic shadows so that you have an idea of what you’re shadows will look like when you are using statically built shadows.
You can also have a look at our Wiki Lighting Troubleshooting and Tips guide here that covers a lot of basic issues: A new, community-hosted Unreal Engine Wiki - Announcements - Epic Developer Community Forums
Feel free to ask questions if you are having trouble. 
Tim
I increased floor mesh lightmap resolution to 512 but nothing changed
Ok, something has changed after set ‘‘Cast Volumetric Transflucent Shadows’’ to true in my mesh settings. I don’t know whether it is required
It only helps with meshes that has translucent material. Maybe you just ran into a momentary glitch, in which case it often helps to restart the editor.
Ok, thanks a lot for help! Everything works perfectly now!