External webcam shows only noise

I've got a Blackmagic Micro Studio 4K camera as my input connected via HDMI.  It's worked before and all was well.  Today, though, I was getting purely noise (with image ghosting).  Tried on Google Meet and the camera worked just fine as an input source.  Went back to Zoom and still had the same noise issue.  Restarted zoom, turned camera on/off, unplugged cables, and restarted computer, all to no avail.  Any ideas?

Mac OSX 10.14

Zoom 5.9.1