I can also tell you that if you are working with file numbers in the 10,000, windows will notoriously interfere with their built-in services. When copying or moving, msdefender might delay every file copy because it marks the action as suspicious and begins scanning the files beforehand. And also the trkwrks or however that drive observation service is called may block actions on specific files just because.

In short, you are not only fighting drive formats at that point, you are also fighting your built-in system services. Source: I wanna die.