mask option not working in color correction fcpx

The mask option in color correction of fcpx 10.2.3 is only working intermittently. When I add color correction sometimes I can hover my mouse over the color correction tab in the inspector and the mask icon appears, other times it doesn't. If I close and reopen fcpx it comes back for a while and works fine. Not sure what is going on with it.

15" macbook pro, 266 GHz, core i7, 8GB ram

El Capitan 10.11.6

fcpx 10.2.3