It's virtually impossible to tell without getting a look at your full timeline, effects, keyframes etc - but one thing that comes to mind is: could you have possibly set a 'hold' keyframe/s? This keeps it's value until the next keyframe, rather than iterpolating between keyframes, and could give the impression things are not updating.
See 'keyframe interpolation methods' a little way down this page: Keyframe interpolation in After Effects
Hit U on the keyboard with no layers selected to reveal all your keyframes.
Thanks for the link, I'll take a look at that and see if I notice anything. Now that I've had time to think and learn a bit more, I probably messed up some obscure thing in the creation of it because I was experimenting with everything else. Thanks again!
Sorry for this issue. Did you ever find a solution? Please let us know if you have or if you still need help.