70ms is too high for control rate fluctuations.
And the control rate will also affect midi output in the same way… and keys etc, and we’re not seeing 70ms there.
I suspect, it might be possibly related to how the exp comes from the micro controller then to mother host (via serial) , the mother host to pd (via osc).
However I’m still surprised this is anywhere near 70ms, given keys are doing the same thing.
Perhaps need to check the code, and see if for some reason the exp pedal is treated differently?!