New instrument in M4 doesn't appear in the mixer and is muted for playback

Hello
I needed an E-flat Wagner Tuba and created one in the instrument file by copying the F-version and changing transposition and designation accordingly. So, in the example below, the F-tuba is a working instrument. The Eb version appears in the instrument list, transposes correctly and looks fine, however - it does not show in the mixer and is completely muted. Is there something I have forgotten?

              wagner-tubas
              Wagner Tuba
              Wagner Tuba
              Wag. Tb.
              *F
              Wagner tuba in F.
              brass.wagner-tuba
              F
              1
              35-74
              35-77
              -4
              -7






              wagner-tubas
              Wagner Tuba
              Wagner Tuba
              Wag. Tb.
              E♭
              Wagner tuba in E♭.
              brass.wagner-tuba
              G
              1
              35-74
              35-77
              -5
              -9