Hello!
So far there haven't been any reports on frequent problems, so thanks for reporting! I've been under the assumption that the Mobile Controller built-in tutorial will guide you step by step through the setup, and in the app pressing ? at the top-right corner should show help including some troubleshooting tips. So, in the absence of bug reports I've been thinking that everything is still working as it was when the app was tested before the release.
Well, but let's try to get this sorted out!
To start troubleshooting, just to confirm the basics:
1. Have you enabled the mobile controller in UnReal World setup? (Main menu -> setup) ?
2. Can you verify that your computer and the android device are both connected to the same WIFI / LAN ?