Go to CS:GO Advance video game settings and change from High to Medium (and lower if necessary) to see if that works.
If that doesnt work, reduce stream resolution to 1280x720 at 60FPS Lanczos. Start with 3500 bitrate and test. Work your way up to 5000 in increments of 500 until your system can't handle it.
I would recommend having a second monitor with Task Manager running while you are doing your tests. Watch CPU and GPU levels, performance charts for spikes and overall average levels. You need to know where in the game and at what levels what is the norm and adjust.
If all that fails then you might have to use the AMD H264 encoder.
I would think that a Ryzen 2600 6 core and RX 570 doing x264 is borderline for doing 1080p streaming. With your system, I would lean more toward 720p and lower CS:GO video settings.