In case anyone else comes across this like I did, having trouble with GSAP animating from one clip-path to another: make sure both clip-paths are using the same units, including any zero values.
For example, trying to animate from this:
clip-path: polygon(0 0, 100% 0, 100% 100%, 0 100%);
to this:
clip-path: polygon(-100% 0, -100% 0, -100% 100%, -100% 100%)
wasn't working, but when I changed the zero values to percentages, it worked perfectly.
// From
clip-path: polygon(0% 0%, 100% 0%, 100% 100%, 0% 100%)
// To
clip-path: polygon(-100% 0%, -100% 0%, -100% 100%, -100% 100%)