I don't know if it is just me, but whenever I try to learn a song with many instruments, I can't scroll down the instruments list to actually view the sheet music I want to learn.
Go to the left bar with your mouse and use the wheel to scroll ;)
Is it working for you?
Co-Founder of Jellynote
Not many laptops have scroll wheels.
You've got to zoom out using ctrl + on your computer keyboard to click the instruments you want that are lower on the list.