Looks like that ring terminal has a very crappy connection to the threaded rod. That's what is glowing. That tiny spot that is glowing is all the mechanical connection there is. The entire circumference of the ring terminal should be tightly sandwiched between two washers and two nuts all pretty tight. Its getting hot and glowing because it is trying to transfer a large amount of current across a very tiny spot.
Think of it like this - take your heat gun and run it for just a minute on a cheapo thin lamp style extension cord and feel the extension cord. It will probably be hot enough to burn your hand. Do the same test but with a good heavy duty 12ga extension cord. The cord will barely be warm. Also a good tip - if you do use a heat gun around the shop on a cheapo say 16ga 50ft drop cord, it is struggling and would get hotter and be much more efficient on a much heavier gauge cord.
Remove those ring terminals, wire brush the threaded rod, cut off and properly crimp a new ring terminal onto the wire, use 2 new washers, and get the 2 nuts squishing the ring terminal pretty tight.
Also - on the electronics side near the bottom, make sure the wires connected to the breaker switch are good and tight. On ours one had come out of the breaker and the hot wire just pulled out by hand quite easily.
The only other thing I can think of it maybe the heating element is defective (ours came with a spare in a second long stainless tube) or the heat controller is malfunctioning or something. Still though, with that one small point glowing instead of the entire circumference of the terminal that screams crappy connection to me.
