Some rendering lag/GPU overload, encoding lag, along with lots of dropped frames. Clearly there's not enough bandwidth to send out 8-10 streams concurrently using the current bit-rate. Your LAN looks OK. Try reducing the bit-rate of the streams to 3000 or 2500kb/s see if there's improvement.
Some other suggestions to get you running better:
Disable HAGS
Set Color Range to Partial
Mics are failing in the 2nd log, fix Sample Rate mis-matches.
Scenes have loads of Display, Game, Window Captures. Only (1) per to avoid interference.
1080p Recording:
00:37:58.946: [obs-nvenc: 'advanced_video_stream'] settings:
00:37:58.946: codec: H264
00:37:58.946: rate_control: CBR > CQP
00:37:58.946: bitrate:
00:37:58.946: cqp: 15 - 18
00:37:58.946: keyint: 120
00:37:58.946: preset: p7 > p5
00:37:58.946: tuning: ull > HQ
00:37:58.946: multipass: disabled > qres
00:37:58.946: profile: main > High
00:37:58.946: width: 1920
00:37:58.946: height: 1080
00:37:58.946: b-frames: 4 > 0
00:37:58.946: lookahead: false
00:37:58.946: psycho_aq: false
720p Streams
01:25:25.573: [FFmpeg NVENC encoder: 'multi-rtmp-video-encoder'] settings:
01:25:25.573: encoder: NVIDIA NVENC H.264 (FFmpeg)
01:25:25.573: rate_control: CBR
01:25:25.573: bitrate: 5000 > 2500 - 3000
01:25:25.573: cqp: 0
01:25:25.573: keyint: -1 > 2 Seconds
01:25:25.573: preset: p5 > p2
01:25:25.573: tuning: hq
01:25:25.573: multipass: qres
01:25:25.573: profile: high
01:25:25.573: width: 720
01:25:25.573: height: 1280
01:25:25.573: b-frames: 4 > 2
01:25:25.573: psycho-aq: 1 > false
01:25:25.573: GPU: 0
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