Inconsistent bitrate with movement on screen

[Cozy04]

I've started streaming recently but still have some issues concerning my bitrate. As a bit of info: I have a LAN connection and get ~30 Mbps Upload on speedtests. I have my bitrate in OBS set to 9000 kbps and can sustain it without issues, however as soon as there is any movement on my screen the bitrate becomes super unstable, even if I don't have any demanding programs such as games open and just drag around the OBS window. I'm using the x264 Encoder. My PC specs are: Ryzen 7 5800x3D, RTX 2060, 32 GB 3600MHz RAM. As I can sustain 9k for longer periods of time I don't think it is my ISP that is causing the issue. Has anyone encountered similar issues or knows a fix for this? The log I have provided is from ~40 Minutes testing around and the first ~20 Minutes are just a black screen with audio turned on in the middle. After I went back and forth switching Captures etc.

 

[Cozy04]

Adding some more to this: I have just had ~20 seconds where the same issue appeared while still only being on a black screen. It fixed itself and is now stable again. This might give some more clues as to what is happening