I’d bet it was Stefano’s goons and that he will keep Sydney from EJ. I think EJ had said he’d keep both Stefano’s grandkids away from him if he continued. So, Stefano probably decided to take and keep Sydney somewhere away from both Sami and EJ. He doesn’t really care about Nicole but maybe he’ll get her out of jail and have her care for his grandchild somewhere away from EJ? When her maternity leave is over, she could return with Sydney.