BMPCC 4K to Hyperdeck Plus not working

Got a nice little cart set up for a TV show, photo from 2022. We have an HDMI computer monitor feed and a camera output (via HDMI) going into two Hyperdeck Plus machines. I'm upgrading to 4K resolution now.
I was able to get the computer monitor feed to record at 2160p, but the Hyperdeck won't record the signal from the camera at 2160p, even though the settings seem to match on both machines (2160p, 23.98, prores proxy).
Nothing I try seems to work. Could it be that the HDMI output from the camera is not at 2160p?
Thanks in advance for your help!