Question: Recording 4K in camera not possible with ATEM SDI

What I want to do:
- Record and create a Davinci Resolve file with the ATEM SDI Pro ISO
- Internally record 4K in four cameras (2x BM Ursa Mini Pro 4.6K g2 - 2x BM Pocket Cinema Camera 4K)
- Change the HD ISO files in the project from the ATEM to the 4K in camera files and export/render the project in 4K

Last weekend I had a project where I rented the ATEM SDI Pro ISO, I tried to do the things listed above with 2 BM Ursa Mini Pro 4.6K g2 camera's. The moment I switched to 4K for the in camera recording the video signal cut out.

Is there a possibility to make this work?

I have been planning on using my BMPCC4K in the same way, so after seeing your post, I tested it. I have an ATEM SDI Extreme ISO and a Pocket 4K. I plugged a HDMI cable from my camera into "HDMI IN" on my Bi-Directional Converter. Then "SDI OUT" into Input 4. From Output 3 of the ATEM, SDI to "SDI IN" on the Bi-Directional converter. My Atem is running the latest software update 9.5, and the converter 9.0.1

I set my camera to UHD RAW, and the ATEM is set to 1080p 59.94 It works perfectly. The camera recorded 4K internally and the ATEM recorded 1080p

I can confirm I also frequently record camera originals with a Pocket4K and an Ursa Mini Pro G1 with Bi-directional converter into an ATEM Mini Pro and ATEM Mini Extreme ISO and never had problems recording 4K in camera.

Last weekend I had a project where I rented the ATEM SDI Pro ISO, I tried to do the things listed above with 2 BM Ursa Mini Pro 4.6K g2 camera's. The moment I switched to 4K for the in camera recording the video signal cut out.

Did you also set the SDI output resolution to HD? The Ursa Mini's will happily output 4K over SDI, which the ATEM SDI's won't be able to receive.