I agree, it sounds to me like the Bass player is phoning it in.
He maybe thinks the songs are too easy, and don't require any effort on his part? I've run into players like that before.
In any case, I would talk to the drummer about it. Since he's friends with the guy, maybe he can talk to him about it.
If it's not resolvable that way, I would look for some other players who really are interested in playing the same kind of music.
The Lone Ranger and Tonto were ridin' down the line
Fixin' everybody's troubles - Everybody's 'cept mine
Someone must have told them I was doin' fine...