Turns out Colour Management is broken in Windows 11 (unless you're on the Insider Programme where it's been fixed) but in a nutshell a lot of programs can't read custom calibration profiles.
So next question - am I likely to encounter issues if my Workstation is windows 10 but my render nodes are windows 11 when rendering through DR? Ideally I can just roll back the workstation to W10 and save myself a tonne of time.