At one distinguished region the separation appear curved. The pH-gradient, visible by the iso-pH lines, nearly breaked down at this place.
The contact between the platinum wires of the electrodes, in most of the cases it's the cathode, is not working properly:
No contact, or worse: a “half contact”!
The bad contact zone gets very hot and the Ampholytes cannot bring up the pH-gradiend.
1. Always keep your electrodes clean: Wipe away the dirt with water and Ethanol after and before every separation.
2. Before start of the IEF press the lid (and the electrodes) down on the gel to ensure good contact along the whole electrode wire.