Is this alternator belt installed correctly, or is it inverted?
Re the picture you posted, is this how the "reputable Alfa mechanic" gave you the car after alternator replacement? If so, run don't walk away from this guy.I agree. Nut is missing. I don’t think the belt has ribs on both sides? Do those exist?
I’m sick in bed, when I feel better I’ll take a close look at the belt.