LG Ultrafine Display Sound / Camera Problem

Hey, I´ve got a problem with my new LG Ultrafine 5k Display. The first time I connected it to my new MBpro late 2016, everything works fine. After doing some video chats with Skype, I´ve got serveral problems. Even choosing sound and camera output via the LG, the OS always choose the build in MacBook speakers and camera. Now the sound output and video about the LG dispay doesn´t work at all. What should I do?

I did a reset of my display via the LG screen manager and also reset the USB settings. Any suggestions?