I had a sacrificial board identical to the one in the above image. It wasn't working properly either. I traced the problem to one of the 3 diodes. I replaced the original diode with one that I had in my spare diode container. I used an FR207. It's described as a "fast recovery" diode. Definitely a shot in the dark but ultimately it eliminated the problem. I'd rather have more information to go on to be certain it holds up in the long run.
