After running some tests with the project that was provided I noticed that the mobile device was having trouble finding the default map. I then created a new map and moved the UMG that you had created to that map. After this I went into the project settings and changed the default map to be the one I had just created. This resolved the issue for me. The reason everything seemed darker is because the default map was being brought up (no lighting). Could you try setting the level that you are using to the level that is loaded up by default? Could you also let me know if you receive an error message when launching onto the device?
