Debt investment measured at FVTOCI and impairment loss

Hi all,
As the HKFRS 9 requires that the debt investment measured at amortised cost or FVTOCI should recognise the impairment loss. However, the debt investment measured at FVTPL is not required since it is measured at fair value with gains and losses recognised in profit or loss in the same way as an impairment.

So, why do we still need to recognise the impairment loss for the debt investment which is measured at FVTOCI?

Many thanks