Hey 8!,
So the main issue here is that you might be misunderstanding how Deferred Rendering works within UE4.
With deferred rendering, lighting calculations come second to material calculations. Your reflection capture actors are actually taking a real-time image of your scene and applying it to your material based on their location and the sky information.
With this in mind, I have spent a good amount of time testing and consorting with my teammates. The good news is there is a bug that has already been reported which is the issue you are experiencing.
UE-4936 - Reflection Capture are Not Working with Moveable Directional Light on Mobile
This bug is scheduled to be fixed and integrated within version 4.8. As always, we appreciate our users patience reported issue. Look for the update within the release notes of 4.8 for the fix.
As your temporary workaround, you could continue to use the faked reflections through the emissive channel. If you have additional questions or need further help please let us know.
Thank you,