The russian convention that was shutdown yesterday has released a statement going over exactly what happened at the event. Police did arrive due to an anonymous tip that the event was promoting 18+ content to minors, but when they arrived, they didn't find anything that really broke any rules. They did however request that the convention close up shop early, which they agreed to do. In the end, only about 2 hours were lost over the course of the event.
You can read their statement on it over here, though you will need to use google translate since it's in Russian.
