Might be, but I think it's software. I've got a Blackmagic Intensity Shuttle TB feeding into a Mac Mini I've got outfitted with an SSD. The real-world perf floor should be 208MB/s read, 235MB/s write. I've captured clips in 10bit lossless via their built-in Media capture application, and haven't noticed issues (I haven't been leaving it running for long-form stuff aside from VHS transfers, so I dunno if there's the similar issue and I have just not seen it before.)

To save my sanity and space, I've been trying to import it through Final Cut 7 into a lossy format, either ProRes or Motion JPEG, either of which is much smaller than uncompressed… but it's still fouling up.

I've got a Kona LHe cap card that came with a new computer I bought so I need to scrounge up some HDMI to SDI converter box and see if I get better results with that. I'll figure it out eventually…