Netflix on the PC no sound?

I have a very weird problem. I use an external USB amplifier for my headphones and this works everywhere without any problems with any program. But if I want to watch something on Netflix then I have no sound at Netflix and then suddenly no longer synonymous with all other programs. The picture but at Netflix is running. At Spotify z.b. I even get an error message that I can't play at the moment after I wanted to watch something at Netflix. Restart does not bring much because I can watch as usual all programs except just netflix again.

I have exactly the same problem