Besides a possible issue with poor connection inside the device, which is noted in the referred to discussion thread, it is very possible that the unit plugs in very close to the heating element and the heat generated by the element is transferred to the plug. With a smoker, this heat would be much more constant that say like a electric skillet or frying pan which are only on for a short time. These have been hot to the point that I do not remove them until the unit has been off and cooled down.
An extension cord being used with the device, especially a 16 gauge one, will add to the heat as the cord will heat up and does not act as a heat sink, but that is at the end that would normally plug into the wall, not the end shown unless the cord is very short. 60 foot (about 20 meters) extension cord and a constant load at 12+ amps is not a good combination.
Another possible issue is where this is being used. Whereas a frying pan would be used in a conditioned space and such connections are benefited by such, I am not so sure I would have a smoker in my house. What is the temperature where it is being used? Is that ambient temperature outside the ambient temperature operating range of the smoker?
A final cause can be moisture or extremely high humidity.
There may be other causes that I have not thought of, and mayhap the designer did not think of these issues or those above.