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Midi export is quite 'nervous' atm.idk hw to export it to midi.
You can export single tracks, and that works ok, but as soon as you have several tracks, then some may get lost.
You should be able to export single tracks, and then combine them in a midi-editor like Free Anvil-studio I would use a copy of my project, and not the Master. Then you are at least sure not to loose any data