I am downloading and installing the latest Nvidia GeForce-driver now, to see if that helps. The file plays fine in QT, and even the DnxHD-copy I made of the video using Blackmagic plays fine in QT. The original video-file I received from my client is only 14mb. Link:
https://drive.google.com/file/d/1vrG...ew?usp=sharing
But please don't waste your day spending too much time on this issue!