Can't enable solo buttons all of a sudden!

[Rosetree]

Hello.

I don't know what setting or action I messed around with, but no matter how I try to enable the solo button for your selected track, it gets lit for a split second and goes back to the unabled state.

Mute buttons work as intended for all tracks.

I am sure it has to do with a very basic setting that I am not currently aware of, so if you have any idea as to how to solve this, it would be greatly appreciated!