I still have this issue on 4.10.4. My text is not displaying on my iphone6. It does display in my preview.
Another weird thing is that if I build my project from unreal installer, it shows up on my device. But if I build from unreal source on github, my font does not show up on my device.
I also get this message in my xcode console:
Feb 26 22:59:39 Joshs-iPhone
SWShooting[1612] :
[2016.02.27-05.59.39:245][
0]LogSlate:Warning: ‘Roboto’ does not
provide a composite font that can be
used with Slate. Slate will be forced
to use the fallback font path which
may be slower.