Try disabling MIDI thru (on the keyboard and on PT).
Maybe a MIDI loop (?)
If MIDI goes out to keyboard from PT, gets routed back (via Thru settings) from the keyboard to PT, and PT in turn forwards it to the keyboard .. and the keyboard returns it ..
doesn't take long to see how this could be problematic.

Wierd thing is that from the description this seems random. Random always complicates things. From math problems to computer problems.
See if you can do a little troubleshooting and narrow it down.

When a file does this, open another file, then re-open the file that had problems.
See if any settings seem amiss before hitting play (check Thru settings mentioned above for one).

It probably isn't a random event, there is likely some setting that changes. We just gotta find it. Maybe the original MIDI had a sysex message or controller message and it has been inherited in the seq files.
Lots of obscure ways this could happen. But we need more clues.


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