Why does this clip go green and how do I fix it? I have a 4k clip in after effects, in which I have used the Keylight effect. The shot looks like this (I have to blur the face for privacy reasons):

Anyway, but in some frames, towards the end of the video, the shot flashes briefly to this and back to the original:

This sometimes happens during preview while I am working if I start running out of RAM, but I don't know for sure. Sometimes, the shot stays green like that for quite a while before switching back.
I have had this happen in other after effects projects that were not 4k...
I don't know what is going on. Can someone please tell me how to fix this?
This happens to me sometimes using Keylight.  I find that if I make a tiny adjustment to the settings (holding down CMD and dragging on one of the controls (eg Screen Gain or Screen Balance), it usually disappears.