I'll assume that you're not using a dedicated server, but just hosting each gameplay session from the PC?

At the Start Game screen, with the list of worlds, there are three radio buttons: Start Server, Community Server, and Crossplay. This is going to sound really dumb, but make sure that Crossplay is enabled before you start the server.

If it's not that, go to the main menu on each system and in the bottom right corner you should see the version build number. It's currently 0.214.300; be sure that they match.