When a Directional Light is changed from static to movable, the materials in the level will appear dark.
1) Open the CL version of UE4.
2) Once open, open a New Blank Template with the Starting Content included
3) Once the level loads, Delete the table and chairs within the level.
4) Select the Floor in the level and change the scale of the floor to (5,5,5)
5) Once that is complete, In the content browser, find the SM_MatPreviewmesh_02 and drag one into the level
6) Once it is in the level, locate M_Metal_Burnished_Steel
7) Place this material on the mesh and on the floor in the level.
8) Switch the directional light in the level to Moveable.
9) Place a skylight into the middle of the platform and make it static
10) Click on the Build button in the toolbar
11) Play the level in Mobile preview
12) You can also deploy the project to a mobile device and see the same issue occur
Head over to the existing Questions & Answers thread and let us know what's up.