Unable to load city due to missing addon

Hello, 

was playing for some time with my friend on private region. Then from some moment the game started to complain, that my city is not working as needed and has to be loaded to previous working state. It was doing it like every 10 minutes or so. So I decided to leave the city and get it back. And I am not able to do it also now. Now the game says that I can't this city back due to missing addon. Like why? I was playing a lot before this and now I am starting to miss something? Also it doesn't say, which addon I am missing. Please help.