Occasional black frames with Blackmagic Intensity Pro 4k capture

[frisco]

I'm using obs 26.1.0 on arch linux. I have a Sony A6100 camera outputting 2160p29.97 YUV 4:2:2 plugged into a blackmagic intensity pro 4k, and am using the decklink 11.7 drivers. Adding a blackmagic device source mostly works in OBS (after enabling DesktopVideoHelper.service with systemctl), but there's one big problem: every once in a while, I get a black frame, spoiling the video.

Some other possibly relevant observations:

• The only Mode that works in the properties screen is "Auto". If I try setting it to 2160p29.97 explicitly, it doesn't work. I also tried every other setting, and none of them work other than auto.
• The Blackmagic MediaExpress app seems to work fine, without black screens, and confirms that the card is getting 2160p29.97 from the camera.
• The camera and OBS seem to work fine through two USB capture devices, the Epiphan AV.IO 4k and Elgato Camlink, albeit with chroma subsampling.
• The problem persisted in two different PCIe slots, so doesn't seem that likely to be hardware. It's currently in a PCIe x16 slot, because I'm using an AMD EPYC CPU that has tons of PCIe lanes, but same problem occurred in a x8 slot. My motherboard doesn't have any x4 slots.

Nothing shows up in the logfiles when the black frames flash by.

Given that MediaExpress works, it seems like it might be an OBS problem, so I'm wondering if anyone has any experience or ideas. In particular, is anyone successfully using a blackmagic capture card on linux? Is there something else I should test (maybe ffmpeg) or any other advice?

Thanks.