Probably St Elmo's Fire...
I like the NAZI secret anti-aircraft weapon theory. It is a lot more fun.
If it was a weapon it succeeded in a small way by creating some confusion among our pilots but it failed to demonstrate any of it's intended offensive capability and it failed to have any appreciable effect on our radar or radio transmission.
Yep, fun but so unlikely. There is no plausible reason for the Allies to keep secret an ill conceived NAZI idea and no reason to believe that there wouldn't have been documents found describing the weapon after the war.