I’ve been using an Apple Mighty Mouse (bluetooth) for years now, so for years I’ve been dealing with a scrollball that occasionally gets stuck.  As someone who used to use mice that relied on a physical ball for tracking, this is nothing new.  The only real difference is that we can’t remove the scrollball to directly ungunk the mechanics.  My personal preferred way to ungunk/unstick/clean the scrollball (and mind you, for all I know, this might destroy your mouse) is to turn the mouse off, take a q-tip, soak up some denatured ethyl alcohol, and rub it around the scrollball, rolling the ball in every possible direction to try to get as much of the alcohol down and around the ball as possible, hoping to loosen up any gunk in the works there and bring it up top where it can be wiped away.  Typically, this unsticks the ball and brings some visible gunk and stuff to the topside.  It also helps to press down on the ball while rolling it around to ensure that it is moving the mechanical bits with which it has contact.  Let the mouse fully dry before turning it back on.