THE FOLLOWING ALSO APPLIES TO IGNITE FLUID DISTORTION (and probably all other Ignite plugins with an 'animation' tab).
Heat distortion inside Hitfilm animates by itself.
Heat distortion in After Effects has no animation at all in any timeline area that only contains a static image. It distorts the image as expected but the distortion is static, regardless of the settings in the 'animation' tab.
Seems like AE is assuming that nothing has changed on the frame so it just copies the previous frame instead of re-rendering each frame.
Workaround is to put a solid somewhere off screen with a wiggle expression in the position field. This forces AE to acknowledge that something has 'changed' and re-render.
Using Windows with a 4k project.
Steps to recreate (AE CS6) :
1) create 4k project
2) import static image jpg and drag into comp
3) drag 'Ignite heat distortion' onto image
4) attempt ram preview