Reading this thread helped me get it working on my wife’s HP Slatebook X2, but not on my Galaxy S4.
The remark about Miracast working only over wifi made me realize that the wifi connection stored in the box was no longer valid as I long time ago changed the SSID of my wifi, but since the box is cabled it didn’t matter until now.
So I entered setup and selected Wireless connection instead with the updated wifi info. Then Miracast worked on the tablet, but alas, not on my phone.
Furthermore, I can confirm that running the box cabled is no problem to Miracast as it will automatically change to WIFI mode. But of course, the stored wifi info has to be correct. So I do get the best of two worlds! Note: it is a bit more difficult to start a cabled connection as I have to try two or three times. But then it works fine.
As said, my S4 will not connect. However, I can make a Wifi Direct connection to the WD TV Live with it - I just have no idea what Wifi Direct is good for!