When you format it with your laptop, be sure to format it ExFAT. NTFS will not work in the drone.
A bad card reader connected to the laptop might be the problem.
Be sure to stop video recordings before powering off the Mini. Not doing so will render the last video file to not be readable by a player. This could be the issue if only the last video shows as corrupt.
All is not lost however. Just put the card back in the quad, power it up for a minute. That should close/finalize the recording. If that doesn't work, there's a process to rebuild the file with the needed headers.
If you moved the file before realizing you didn't stop the video before powering off, then you'll need to repair the file.