Why does TOS7200 display a flashing “64 V” and “0.25 MΩ” when starting a 500 V test?

The flashing indicates an over-rating condition.
The rated current of TOS7200 is 1 mA. However, at 500 V with a resistance of 0.25 MΩ, the current would reach 2 mA, which exceeds the rated limit.