System Overview:

vMix version: 28.0.x (problem started after updating from v26)
Resolution: 4K 30fps (constant)
Hardware:
3x Blackmagic Studio Camera 4K (via SDI)
ATEM Television Studio 4K
SDI to HDMI converter → DeckLink 4K (PCIe)
CPU/GPU usage < 10% in vMix
Workflow: vMix for switching, output to OBS via vMix External + VB Audio Cable, OBS as encoder (only stable method so far)
Internet: High-speed (700 Mbps), stable (problem persists even in ideal network conditions)
Symptoms:

Yellow stream button after ~30 to 90 minutes
YouTube stream freezes (buffering wheel)
Logs show:
real-time buffer [vMix Video YV12] too full … frame dropped!
or av_interleaved_write_frame(): Error number -10053 occurred (rare, at home)
CPU, GPU and Render Time are consistently low
Happens even without live input, e.g., playing a 4K MP4 for 2 hours produces same result
Reproducible across multiple locations and networks
Tested:

Network seems not to be the only cause:
Same issue occurred to a colleague in a different company, using different setup but same vMix version (27+)
Streams in Full HD also fail with yellow button (even with low bitrate)
Streaming from OBS directly — works fine (even in same network/machine)
Streaming over Wi-Fi works; wired connection fails (same internet access, different adapter)
Hypotheses:

Regression in vMix 27 or 28 RTMP encoder/buffer handling
Interaction with:
DeckLink drivers (via DirectShow?)
Video buffer overflow due to internal mux/demux issues
Potential issue with GPU drivers or codecs (some Reddit users resolved by updating NVIDIA drivers)
Possible stack/network incompatibility with Windows 10 — but not confirmed
Tried:

Adjusting bitrate, resolution, audio formats
Different cables, converters, capture cards
Contacted vMix support → Response: "machine, hardware or internet issue"
Next Steps:

Planning to test with vMix 26 again on the same machine
Full GPU and OS driver update (possible move to Windows 11)
Monitoring via Wireshark and external tools

Has anyone else experienced this buffer overflow / dropped frame / yellow stream button behavior after upgrading from vMix 26 to 27 or 28?

Any insights on RTMP engine regressions, driver issues, or encoder tuning would be greatly appreciated.

Thank you,

Gabriel