Don't know about the one that just quit shooting but the one that went off when closed is a common problem with ks-5s== there is an adjustment screw you reach thru one of two holes in the trigger guard that you turn to put it back in time--don't remember if you turn it right or left but about a half a turn is all it takes--fixed mine fine.
Not unusual for Krieg's to break down now and again. New a buddy had one break down in a shoot off. Scared the h e double toothpicks out of everyone when he closed the gun and shot the trap house. Only shoots the other K gun and hasn't had a problem in 5 years.
If the first example had a KS-5 Special, it has an adjustable trigger, both let off and weight. If you thoroughly clean that gun and re-adjust the "cripness" of the trigger (let off) by setting it while disassembled, you'll likely have the situation you describe; gun fires when closing it. A turn or so on the adjustment screw while all assembled will solve that one in 10 seconds. Haven't a clue why the 2nd issue but any gun can have a fatal quit with a broken part. My "special" just keeps working right so I doubt anyone would call "all" of them suspect....breakemall....Bob Dodd