If a player on the same device as the server joins the game and leaves, that player won't be able to join until their Minecraft UWP app is restarted or the server restarts. This can be observed in the video attached.

The console does log that the player has left the server and no additional messages are logged when attempting to rejoin.

Update
Disconnecting from any game whether locally hosted, network hosted or on a server, the player is unable to reconnect to a server hosted on their device.