Streaming in 1440p/1080p+ 60 FPS does not work properly.

Yo I got nitro and would like to stream in 60FPS, but if I start the stream it doesn't remain in 60fps really. It sometimes even starts lagging so hard after a few min that I have to restart the stream and then in works fine?

Is it possible to stream in 1080p60fps or 1440p60fps? In OBS it does work... 

I reinstalled it already.

I have an 200k Down / 50k Up internet connection.

PC:

CPU : Ryzen 7 1700 @3.8Ghz, GPU: GTX 1080, RAM 16 GB