What caused my electric deep fryer to overcook violently?
As you cooked by batches the last one add brought much more water than usual because


it was the last portion of the pack and usually ice pieces are coming down as well
the frozen balls kept condensing water on them for all time you fried the first batches. 


Except if meantime you have discovered a malfunction of the fryer so that the T goes so high at the heating element to cause the oil to start fuming.