What could be the reason for one loop being significantly more power hungry on an SP20?
Copying asker's own answer, so that this question can be removed from the unanswered queue (assuming this answer gets upvoted).


  I have found out how to get rid of the problem: Setting the start volt 0.05 below max. voltage on all loops seems to have made it more stable and the problem vanished... I still don´t know how it came about but at least I found a workaround :)