Make sure that you registered with the same authentication process across all of your devices. If you used different methods to create an account (e.g. email/password on one device and Facebook on another), it is likely that you created two different accounts. If you used an email/password combo, they also must be the same across devices.
Verify that your mobile devices have access to your computer. Open younity Settings on your mobile device. Does it show your computer in the list of Devices? And does younity say that the computer is available over LAN or Remote? If not, then you need to ensure that computer is online and connected to the Internet.
Verify that younity has finished scanning the contents of your computer. Hover your mouse over the 'Y' icon in the Mac menubar or the Windows System Tray. A tooltip should appear. If the tooltip says "younity is scanning....", younity is currently scanning your computer. If the tooltip says "younity n.n.n.n" (i.e., younity and a version number), scanning is complete.
Depending on the number of files you have and your computer hardware, it may take a while for the scan to complete. For comparison, a MacBook Pro with a 2.2 GHz Intel Core processor that has 28,000 files and is connected to wifi takes about 20 minutes for the file scan to complete.
Is younity still downloading metadata from your computer to your mobile device? Once your younity computer scan is complete, open younity on your mobile device. If you see a little popup that says "Downloading metadata", younity is still updating the mobile device with the contents of your computer. Once the popup disappears, revisit the Files, Photos, Music, and Videos views and see if anything appears. Note that you may need to manually refresh the view by pulling down on it with your thumb.
Is younity still not showing your data? If, after checking all of the above, you still don't see any of your computer's metadata in younity, there may be a bug, in which case you should let us know. Please visit our forums for help from our staff and your fellow users, or feel free to file a support ticket and we will contact you directly.