Meh… that's exactly the HDMI capture I got months ago. I needed it mostly to debug some Raspberry boot trouble that would show way too short to be parsed by a human before the device would reboot again so it's okay. I did wonder though why the framerate was so jacked up but blamed the undervolted HDMI splitter (It came without a fitting PS so I'm happy that it does _something_).

Lesson learnt. I suspect similar for a dead cheap SD-card writer at work.