Decklink 2160p2997 not supported?

Hi.
I have a Decklink 8K Pro working at 2160p2997
CG titles work fine, except for video playout which studders. I do get a:
warning: device supports video-format with conversion: 2160p2997

Config file is all at 2160p2997

Any clues?

Thanks

Stuttering is usually a sign, that the system is not able to process the video data fast enough. What are your hardware specs?

Thank you. Tis machine has a core i7 with 32GB, RTX 3070ti.
Playout works fine on other software (ProPresenter) but not on CasparCG. Everything is configured as 2160p2997 and the video matches this. It is a very light video H264. VLC also plays it fine., but on Caspar it struggles and audio is out of sync, as if the config is incorrect

Thanks