Regression - reproduces in 2017.2.0b2 ( in 2017.2.0b1 works fine)

Think that when you exit Play mode while your Host is active - something is not cleaning up. To fix the problem you need to restart Editor.

How we can reproduce it using the example you attached
--- please see attached video for more info ---
1 Open attached project and press Play, Lan Host (important - do not press Stop (X) )
2 Press Play button again to exit play mode
3 Press Play button and press Lan Host

Actual result: the player is not created and there is "Client Ready" button

Expected result: Lan Host should work fine even if you previously exited Play mode in the middle of the game