Flash problem in rendering with fast settings

I managed to cut down the CC charater + HDR Light Studio scene rendering times quite fine:

But see that one frame flash. Its ruining the shot :/
My settings are:

Rendered with 130 samples + 5 motion blur subframes, rendering time 2 min 40 sec with RTX 2070 Super.

Is my only option to fix that flashing to raise the rendering PT samples?

I raised samples to 250 and motion b subframes 8.
Rendering time 9 min and flash is gone.

I lower down now the samples until I get the flash again.
Also I see that here the skin details are preserved, something is lost the first render since the samples are so low = subtle noise all over.

130 samples
10 Mb subframes
Optix 0.4

Rendertime 5 min 30 sec.

But now how can I kill those tiny tiny white fireflies on her cheek?
Heheh never ending tweaking sorry!

Hi @pekka.varis! Apologies for the very late reply. The development team was able to reproduce this error and they have been working on a fix for it.

(For you reference, internal ticket #OM-43245)