To "remaster" some of the MIDI files I have on my computer, I've installed Waveform Free and downloaded some VSTs.
So I import a MIDI file into my Waveform project (into separate tracks when asked for it), and adds a virtual instrument to its tracks (OT Strings), which works great for Track 3. However, for the rest of the tracks (4, 5 and 6), it does absolutely nothing. There is no sound playing for these. On the attached screenshot, you can clearly see that there are notes for these tracks which are supposed to be played as well.
Thanks in advance, I'd really like to turn these MIDIs into high quality music files.

