I havent used a kooima front feed roll but I have been in the same situation. Was averaging 1 jam up a day for 3 days then all of a sudden the kemper kept jamming and jamming for no apparent reason. Lowered the metal alert sensitivity and that helped somewhat.
There are 2 half moon shaped wear plates that bolt to the frame either end of the feed roll make sure there is plenty of clearance and they are not loose we have had them come loose and rattle on the feed roll before wich will trip the metal detector.
We had that happen once and the magnet inside the roll had come loose and was rubbing on the roll causing the metal alert. It was a while ago but I think there was no external indication that it was the problem.
Then I can't help you. Seems we've had a lot of "phantom metal" in both our claas and deere. With the claas usually we just have to hose down the feed rolls with water cause some small particles of metal got stuck on the rolls after sharpening knives. We never had that problem with the deere though. Wish I could be more help to ya.