The only thing I can imagine is that C1 doesn't support the specific back resolution that your DNG file is (this seem unlikely given the Phase range). Or that PhaseOne have included a "if camera manufacturer is Hasselblad then stop working" in their code, and given the turbulent history of the two companies this doesn't seem impossible.
it is certainly the reason
I have a few dng from H4D 60 and Capture one doesnt even find them, like hidden files, no problem with lightroom