First of all you should try to calibrate your Expression Pedals. Already during calibration I noticed, that my Expression Pedals barely changed or did not change the values at all for about 40% of the way. So then I tried a suggestion by orb451 and checked the sensor and the corresponding LED. To do that you need to follow these simple steps. Notice: I do not take any responsibility for any damage at all.
1. We need to open up our Board by unscrewing these 16 screws. Notice that some are longer than others, just keep that in mind when reassembling the unit.
2. Flip over the metal cover carefully. The ground wire is attached to it. You will then see the 2 sensor units. For each, remove the two screws to free the units.
3. As you can see my sensor and my LEDs were bent slightly. Just apply a bit of pressure to realign them correctly.
5. Now put everything back together. If you want to know how this system works: The LED sends out light through a semi permeable plastic. Depending on the position of the expression pedal this light intensity is picked up differently by the sensor because the plastic has a gradient on it which blocks light. Depending on the position of the expression pedal and thus the position of the plastic, more or less light is being let through and picked up by the sensor.
This might fix the problem for you. Unfortunatly it did not fix it for me and I had to return the unit.