Midi-ox should allow saving data to a midi file. Just put a block of data there, try playing something similar to what you did when you first noticed the ptroblem. With a mix of fast and slow playing.
Then post (attach) the midi file, note that you'll need to ZIP the file, as I don't think the forum system will accept a .mid file extension. Yes, that's daft for a midi forum! Also note that there might be a problem with .ZIP, but .zip is OK (or was that another forum ??).
As for there just being note ON data, many systems send Note off as a Note on instruction but with velocity as 0. I'm not sure how MIDI-OX shows this. The example in the earlier thread does show these as 'Note Off' with Velocity as 0, the faulty ones though have a velocity as C0 (hex) which counts as Note On when this data should be 00.
As long as data has a couple of examples of 'missing' Off instructions it'll be a big help.