According to
this article, Sergey confirms that there is a conflict between him and Smash's producer who is also Vlad's father. They are basically accusing each other for the break up, Vlad's father says that Sergey wants too much money, and Sergey says that it's not true and that Vlad's father threw him out of the band.
Sergey confirms that he's going to focus on his solo career from now on.