Gabiel Yu,
The (main) cause is the use of multiple montors, but unplugging one/more is hardly a good cure.
It is the top subject in the forum right now, and our staff friends are working on it. One (only) has reported that updating to the latest build of El Capitan and CC 2015 (CC 2015.1) has cured it, but no one else seems to have been able to reproduce it.