Found out that EMC was not an issue, but the LED power supply. I added a 10k resistor in parallel to the 0-10V input which fixed the 0V problem.
Only poor thing now is the bad behaviour of Mervis with the AO extension board. I added a ramp for smooth dimm up and down, but it's actually not smooth but rather stepwise:
Any idea how to fix? Maybe the problem comes from the transformation "to_uint(real)" ?