Your log (which you should review/scan) shows bandwidth issues
The OBS log can NOT see what else is going on with your PC, nor your local network. Make sure your PC, or other devices on your LAN, aren't consuming upload bandwidth that isn't available. IF your Internet connection is wireless (cellular, etc), then other neighborhood users may be contributing to WAN congestion.
If you do real-time network traffic monitoring at your WAN connection, and confirm NOTHING else is using your Internet connection, and you are still seeing such bandwidth fluctuation/contention, then likely you'll need to work with your ISP. A high-end PC is meaningless in this context if your upload bandwidth is limited (or you have competing network traffic from your PC)