Hi Tonza, welcome 
I had a similar issue with my Leaf not responding to the calculated pilot signal in OpenEVSE. I wrote some external control software to manage the openEVSE pilot signal and soak up excess grid power rather than rely on the internal PV divert function. You can find the thread and links to GitHub here:
I don’t actually know if this is an issue with the car or the OpenEVSE or it’s just ‘normal’ 
. It doesn’t matter since the software forms a closed loop feedback path to overcome any offset issues like this. So long as changing the pilot causes the actual consumption of the vehicle to change in the same direction it should work. When the car decides it has had enough and stops charging the pilot will just float up to max and stop there. Which is fine since this is what a fixed output wallbox would be like anyway. I also included just turning charging on and off into the software e.g. for night time charging.
Stu