I have the same problem here.
This is a new WD TV Live Gen3 and it’s slow to reproduce videos (.mp4 as well) and the menu navegation becomes very slow very frecuently.
I have firmware release 2.01.86 (12/10/2013) and I’m using Windows Share over a wireless network.
A wired connection is not an option in this case and the product specs doesn’t request that. Anyway the WD TV shows 2 of the 3 bars in white so it doesn’t seem to be a wireless network issue.
Do I have a defective WD product?