From the pics it looks like you have your thermostat probe right on top of the substrate next to the thermometer probe. If that is the case, then you need to move the thermostat probe. It should be taped (aluminum tape works well) directly to the uth on the outside of the tub.

That way the probe can't be moved by the snake which could result in temp spikes, and it can't get peed on (which could mess up temps), etc.