Cubase 6.05 - score window not showing notes

I just imported a big band arrangement from a MIDI file into Cubase 6.05 Mac.

For some reason I cannot figure out why only some of the MIDI tracks show notes when I open them in the Score editor although all tracks have data.
What could be doing this? Some obscure MIDI messages on some tracks? Some settings I don’t know about?

Thanks

Peter