I agree. The first thing I would do is try to reseat the card. It is short and it does “dangle” from the back of the machine, so if it misaligned the card it could cause a problem.
In this case it might not be a bad idea to use a screw to fasten the card instead of the normal bar bracket in the mac pros. They use normal case screws so finding shouldn’t be a problem and this will lock that board down tight.
If that ISN’T the problem it’s possible that the board failed and needs to be replaced.
You mentioned that you tested with multiple softwares. Did you try in Media Express 2 as well? This will help eliminate any potential software settings issues that may have gotten munged up.
Something to check.
Sincerely,
Joshua
Director of Support
Blackmagic Design Inc.