Mine dropped one star for the first time in a year, which I put down to the level up and graffiti. Training walls cured it, but I am sick of buying and hiding them.
The weird thing is that it went down by 1/2 star when I first logged in, then by another 1/2 star as I was collecting task and property rewards before I bought training walls.
It's why I hate graffiti attacks. Each tag drops you 5 points, and cleaning it up only gains you 1 point, so any time someone tags three of your buildings it costs you 12 points. The glitch made it even worse. I told all my friends that if they pulled the glitch on me that I'd drop them as friends, and I still had to drop 10 of them afterwards.