To sync local files from one device to another, you must be actively logged in to both devices with Spotify open and on the same network
Local files can be turned on/off in the Settings menu.
Can you double-check that you've followed all of the support site steps correctly.
It's also useful to double-check that you have connected both devices to the same Wi-Fi.
If that doesn't do the trick - can you try the following:
Add some songs from our catalogue to the playlist as well as the local file/s and make sure they have ‘Show unavailable songs in playlists’ turned on in Settings
Play some music on the device that has the local files to see if it shows via Connect on the other device
Make sure the router supports the Bonjour protocol. If the router is made after 2005, it will likely have this protocol. The best way to handle this is to check the router make/model and Google it
Another useful step in is to change the source folder of the local files on the pc. The steps are: Uninstall Spotify on both devices > create a new folder somewhere else on the pc and move the local files there > install Spotify again > remove any potential source folders and add the new one > download the playlist again.
Keep us posted. We're always one reply away.
Help others find this answer and click "Accept as Solution".
If you appreciate my answer, maybe give me a Like.