Q: color board preview problem

I have problems with fcpx "color board" preview function.

I remember it was running smoothly and the feedback on the viewer and in the scopes was instant, but now it isn't.

When color correcting (regardless if its Exposure/Color/Saturation), when I move the sliders, I sometimes get NO preview in the viewer and NO change in the scopes- they freeze.

I have to go out to "Effects" and turn "Color Colrrection" OFF and ON again to see the changes in the scopes and in the viewer.

What is even more strange is that it's not always like this - sometimes everything works fine and then it crashes/freezes.

Any ideas??? ;-)

I am using OS X Yosemite 10.10.5 with FCPX 10.2.1 on MacBook Pro Retina 15-inch Mid 2015 with 2,8 GHz Intel Core i7; 16GB RAM and AMD Radeon R9 2048MB graphics.