Colour and exposure of DNGs is really wrong

I'm having significant issues viewing DNGs. Their colour is totally inaccurate and it makes FastRawViewer mostly useless for culling them. I'm viewing them on a Windows 11 machine with a calibrated monitor with ICM turned on. This problem only appears in your software and not in Adobe Lightroom Classic.
I am shooting with a Nikon Z9 in Adobe RGB mode in PicoRaw format. I'm shooting HDR brackets at -2, 0, +2 EV. I then turn these in a 8-bit HDR TIF file using Aurora HDR. The TIFs are tagged with the ProPhoto colour space. I import these files back into Lightroom Classic and then render correctly. I then export these files into another folder in DNG format also tagged with the ProPhoto colour space.
When I try and view these DNGs created from Lightroom Classic using FastRawViewer, the colour is washed out and completely inaccurate and not at all like the TIF images that they were generated from. The thumbnails generated are correct. When I import the DNGs back into Lightroom Classic, they are exact matches for the TIF images they were created from.
I've get Colour Management turned on with the appropriate settings. Any suggestions on what I can do to improve this please?