Strange Issue with Expression Control Effects and Precomp

[Marcel Izumi]

I know this is old, but in the middle of 2018 I have struggled with pretty much the same issue:

– A slider Expression Control was rigged to control the time remapping value of a sub-comp, a couple levels down (in other words, a sub sub sub comp).
– The symptom was that when I tested the sliders, they all worked, but as soon as I started keyframing them, they stopped working, i.e. further adjustments to the slider didn’t appear to do anything at all.

I noticed after a while that what really happened is that as soon as there was a single keyframe on the slider, the frame shown of the subcomp in question was stuck to that of the first keyframe. So if subcomp D would show a 7 on frame 7, setting the first keyframe on the slider in main comp A at the value of 7 would get the subcomp D stuck displaying a 7, regardless of further slider adjustments. You can test this by swapping out the first two keyframes.
I read comments pointing toward the method valueAtFrame(), but I was unable to access the time variable of the main comp from sub comp D. But hard coding it to a different frame prove that the sub comp constantly reads a 0 from the main time variable.

What solved the problem for me was the realization that ALL COMPS BETWEEN THE MAIN COMP AND THE SUB COMP IN QUESTION MUST HAVE A SUFFICIENT FRAME RANGE / LENGTH TO ACCOMODATE THE LENGTH OF THE ANIMATION. So if the Main comp is a parent of comp B, which is a parent of comp C, which is a parent of comp D, which has time remapping enabled and rigged to a slider in the main comp, and your animation in the main comp is 500 frames long, comps B and C MUST ALSO be at least 500 frames long regardless of if you have anything going on in them or not. My mistake was that since I wasn’t planning on animating in those comps, comps B and C could be single frame comps. That’s not the case.