That's where you would expect it to go open-circuit from a short-circuit, (ie kill switch). It's the one spot on the coil where the wire isn't firmly touching other wire etc, allowing it to reach a higher temperature. Possibly, using the blue/black combo for the kill switch, you're weakening the wire at that point due to the high current flow during the short-circuit while the motor stops turning.
Then, it could actually fail at any time.
I re-iterate, for the last time, don't use the blue wire for your kill switch. The current flowing through this wire is much higher than that flowing through the white, while the kill switch is depressed.
This isn't a common problem, especially not twice in one week. Either you're getting bad parts or you're doing something wrong. (Not pulling on the wires or anything like that?) Otherwise, the one thing that stands out is your use of the blue wire from the ignition winding to short the magneto/CDI and kill the engine.
... Steve