Italian transportation system goes on strike often, always check news
This goes for public transportation systems, trains, taxis, airports
The public transportation strike normally works around hours people have to go to work, but it often happens on workdays still
They often announce the strike notification beforehand via news, which is not super convenient for tourists. What I'd do is to check ATM's official website which is available in English or it's twitter account for public transportation options, trenord.it/en for train related announcement. Double check with locals if you can