Como este tópico tem mais de dois anos e nenhuma resposta foi fornecida, estou feliz em receber os pontos. Aqui está a resposta que o autor encontrou, seu self (movido aqui a partir da pergunta).
This is the weirdest thing ever happened to me. Here's what I found out:
By itself the audio driver (be it the default "High Definition Audio" from Microsoft or "VIA HD Audio(Win8.1)" from VIA) stops sending the sound to line-out after waking up from sleep mode
If I also execute the hot keys manager from CLEVO (HkeyTray.exe) audio works through suspend/wakeup but doesn't work after locking the screen
Now the best! Inside the hot keys manager's folder (in my case C:\Program Files (x86)\Hotkey) there is a small .exe file called InitHeadphone.exe. As you can guess running it re-enables audio from line-out/headphones no matter what you did (sleep, lock, whatever). It seems to have some dependencies so it must be run inside the folder.
What an adventure folks! I'll try to investigate more and understand why there is such a connection between two pieces of software of two different producers (CLEVO and VIA). It's almost like they are in a symbiotic relationship! I hope this will help somebody. Please let me know if so. :)
Solução alternativa temporária
If your headphones/Line-out don't work after sleep mode or locking the screen and you have a VIA sound card just download CLEVO's hot keys manager and run the file initHeadphones.exe. I still have to figure out why though...
Solução Estável
wspawn from the forum of Notebook Review (thank you! You are still welcome to post an answer yourself) found the following solution:
To prevent the hotkey software from messing with the audio controls / headphones rename the following file: C:\Program Files (x86)\Hotkey\hp.dll to C:\Program Files (x86)\Hotkey\hp_DISABLED.dll.
SOLUÇÃO FINAL
Apparently installing the Hotkey utility from CLEVO (which can be also found on Sager's drivers page) is enough. Latest version is 8.0100. I still have to find a way to fix the problem without installing this stupid program.