Hey JYs,
We will be happy to investigate your issue further, but we ask that you post a new answerhub question with an appropriate title so we can help other users who might be experiencing a similar problem. By making a new post you make it easier for other users to search out the issue and find the correct resolution.
The main difference between UE3 and UE4 is the rendering process. In UE3 we used forward rendering which calculates your scene in a different order than deferred rendering which is built in for UE4.
Deferred vs Forward Rendering
Have a read over both of these pages to get a better understanding of how deferred rendering works versus forward rendering. Let me know if you have questions.
Cheers,