Clips are distorted

I'm working on a virtual choir project and I'm having trouble with images from different clips showing up in other clips (see photo). The problem is pervasive throughout on many different tracks. Please help!

Can you give us more information? What camera was the footage shot with (using what codec). Do the glitches show up in the raw footage or just when it's been loaded into FCPX? What machine are you editing with (including what hard drive & how much space available). Do the glitches show up in the same spot every time or different spots? That should get us started.

First, go to Preferences and turn OFF the background rendering option, never turn it back on ever.
Next, select the Library in the Browser, and in the File menu select Delete All Generated Files... In the window that pops up, delete ALL render files. Quit FCPX, relaunch.