Velocity issue when exporting to midi from MuseScore 3

Hi there,
I downloaded a midifile of Mozart's k217 from IMSLP and imported it into Musescore 3 in order to edit the score precisely (particularly dynamics). I wanted to export the modified score to a new midifile, to be played in a DAW.
Unfortunately, the velocities in the output midifile are all wrong: they stay stuck at 100 despite all my efforts (checked with midi2csv, cubase and ableton live).
Any idea where the problem may come from ? No issue when creating a new file in MS from scratch, then exporting it to midi. Thanks in advance.