Your very good PC doesn't seem to care that it's very good.
14:01:24.430: Output 'adv_stream': Number of skipped frames due to encoding lag: 943 (14.7%)
14:01:24.430: Output 'adv_stream': Number of lagged frames due to rendering lag/stalls: 1338 (20.9%)
[...]
14:01:37.978: Output 'adv_stream': Number of lagged frames due to rendering lag/stalls: 36 (11.6%)
[...]
14:03:40.365: Output 'adv_stream': Number of lagged frames due to rendering lag/stalls: 1506 (30.4%)
[...]
14:07:21.795: Output 'adv_stream': Number of lagged frames due to rendering lag/stalls: 865 (21.3%)
[...]
14:11:02.413: Output 'adv_stream': Number of lagged frames due to rendering lag/stalls: 46 (1.6%)
[...]
14:12:13.471: Output 'adv_stream': Number of skipped frames due to encoding lag: 33 (1.0%)
14:12:13.471: Output 'adv_stream': Number of lagged frames due to rendering lag/stalls: 795 (23.9%)
Are you able to record without skipping or lagging frames?
Your settings are all over the place in that log. Try these settings:
Video
(Settings > Video)
Base (Canvas) Resolution: 1920x1080
Output (Scaled) Resolution: 1280x720
Downscale Filter: Lanczos
Common FPS Values: 30
Output
(Settings > Output)
Output Mode: Simple
Stream Encoding
(Settings > Output > Streaming)
Video Bitrate: 2500 (if you're not partnered)
Encoder: Software (x264)
Audio Bitrate: 160
After changing to these settings, try again and post a new log.