Open Mission Control
Use any of these methods to open Mission Control:
....
- In OS X El Capitan, drag a window to the top of the screen.
https://support.apple.com/en-us/HT204100
I'm using a window snapping/resizing app and this feature above, introduced in El Capitan, is being triggered instead. This when I snap a window to the center top of the screen.
Is there a way to turn this feature off?