The 6 ohm load resistor in parallel with the LED is probably causing the voltage to drop too low. That LED bulb in parallel with the 6 ohm resistor probably results in a resistance of 5.4 ohms, ...

The basic resistor load bank consists of resistors R1 through R5 and switches SW1, J1, J2 and SW2. Switch SW1 is used to control R1 and R2, while switch SW2 is used to control R4 and R5.

The CSM3637Z Bulk Metal Foil surface-mount, Power Metal Strip current-sensing resistor specifies a load-life stability of ±0.2% at +70°C for 2,000 hours at rated power.