I was skeptical at first of musical instruments that don't allow you to specify the notes you want to play, but it's actually quite functional! The sequence of notes makes it easy to improvise rhythms and melodies that make sense, and it's nice to have both instruments in the same key. It would be neat to see more instruments added!
Update for Version 2.0
It seems that all the instruments are now for "debugging"; for example, the harmonica is now "Debugging Harmonica." They don't have textures, and I can't place the banjo or the piano. However, they still play. I would post a bug report, but the repo isn't publicly available...
Oh, I think there's an issue with the mod settings. The instruments you remember are still there, but just not active due to your settings. I set up the mod so that you can disable individual instruments that you don't want in your world. The fix is to go to Minetest settings and go to the mod settings section, find the Musical Instruments tab and disable, then re-enable each item there. I am trying to figure out what causes this bug so I can fix it. To make it easier to report bugs like this, I have published the repo online at https://gitlab.com/MadKamel/minetest_instruments. Thanks for the review!