07-08-2018, 12:51 AM
Buildings like mines reduce happiness, so it's possible that people working there drop a star while at work. You can try building wells around the quarries/mines/heavy industry types of buildings. It might keep people from getting unhappy at work and allow you to reach that global 5 star.
It's also entirely possible that you have that one grumpy person in your town whose (buggy) happiness never updates and stays stuck on 1 or 2 stars, whatever you do. In that case you'll have to wait for him/her to die.