I installed the same pedal yesterday, which I bought used. I had a different problem, but maybe it has the same origin:
Please take look at the jack of the pedal. Is it a stereo type, TRS jack or a mono, TS jack? Mine has a stereo jack.
I found out that the TF showed a "0" on the heel position of the pedal, but the maximum value when in full toe position was only "82" instead of "100".
So I read the manual and it said the exp. input on the TF is for TS type, mono jacks.
What I did was I soldered together the contacts for tip and ring at the pot inside the expression pedal. That solved the problem. I couldn't assign values to the "100" position, which could be a reason in your case, too.
Just an idea, check it out.
For the Eventide people: if you haven't done it already, please let your customers know that this problem can occur with expression pedals that have a TRS type output cable. Connecting tip and ring solves the problem.