No bass though the index says there should be

Hi,

thank you for this website and all the cool cdlc. I have a problem and I don´t know if I´m doing something wrong: in several songs, e.g. all Blues Brothers and Queen´s Don´t Stop Me Now, the bass is indicated as a series of flat yellow lines or nothing at all, and when starting the song it won´t play any notes either. The cdlc descriptions say there should be bass parts...

Am I doing something wrong?

Thank you!