I have same issue since 7 came out. Updates no resolving problem.
I9-9820X, 32GB RAM, M.2 Samsung EVO 970 PLUS SSD,
Blackmagic SDI DUO 2
Blackmagic Intensity 4K
Tested with Nvidia GTX 1070, GTX 1080, AMD RX590
Tested with diferent drivers.
Strange, that nobody talking about this.