USB 2.0 ports and USB 2.0 flashdrive. Thanks for the program link; quite useful.

I now think there is a glitch with the files themselves, as you say, not all mp4 are the same. Have copied to an alternative flashdrive and the same thing is happening, and I know this fd is pretty good, only because I have never encountered any problem.

Also copied a different TV series to the same folder on the flaky flashdrive, and they all played just fine.

Will find the episodes from a different source and/or just watch it on catch-up somewhere rather than save.