This is really strange.
The expression is working, but is using the comp duration instead of the layer out point.
When I applied it to a different layer inside a different comp it behaved as expected. It’s only doing the odd behavior on this particular layer.
I even tried creating a new variable, but even with that, it goes all the way to the end of the comp.
oP=thisLayer.outPoint;
fadeDur = .5;
s=ease(time,oP,oP-fadeDur,100,0);
[s,s];