Just because the thermostat is set at 93*F does not mean that the heat tape is 93*F. There can be hot and cool spots on the heat tape, or if you have a lot of air around the probe, have attached tape to it, or it even fell out because you moved the rack or tub, it can cause the probe to falsely read low which makes the appliance overheat.
If you get a temperature gun or IR point thermometer and measure the temperature of the floor of the plastic tub over the heat tape, what does the thermometer say?