Last year in mainland Italy I bought a TIM SIM card for my phone and it worked beautifully.
This week I bought the same one in Palermo, and four return trips to the phone store after it didn’t work properly, I ended up exchanging it…no further charge…for a Vodafone one, which works perfectly for everything I need.
Different place, perhaps different cell towers.
So in Sicily, stick with Vodafone.
That's one reason why I prefer to travel with my regular phone and SIM on a roaming plan, as my phone accesses various networks. I'm not sure what criteria the phone uses for selecting which network to roam onto when several are available. It may simply select the strongest signal, or it may prioritize one network over another depending on the roaming agreements?
I had considerable difficulty with Google Fi in Rome in February and March. It didn't seem to allow me access for every available network, just perhaps two of them. I think I ended up using TIM after selecting it manually on those occasions when the automatic selection left me with no service. I have no idea what was going on.