I could not programme all three sockets at the beginning. I unplugged everything again and started with the 'problem case' (plug in for a few minutes and then start programming), then everything worked. It's been running smoothly for more than a year now...
For me, 2 out of three did not work. Galaxus sent me a replacement package with a new set of three. However, I did not have the time or patience to 'programme' the new set. The package is unopened in the cupboard.