Hi all,
Just try to remove the ifi iPurifier3 at the USB1 type B input at the back of my Bartok, and reconfig Roon audio device with “Load Default” (which is “renderer only”, enable core decoder).
Then try to playback MQA CD rip, and Tidal MQA as below :
Tidal with first unfold to 96 by Roon core decoder
dCS detect MQA flag and use MQA filter
MQA CD with first unfold to 88 by Roon core decoder
dCS detect MQA flag, second unfold by renderer to 176 and use MQA filter
So the Roon core decoder + dCS renderer works correctly now, and also trigger the MQA filter correctly 
To double verify the cause, I insert the iPurifier3 to the USB1 type B input again, and repeat the test. The MQA is still working fine. So I wonder it is the unplug and re-plug of the USB cable fix it.
But right now, if I click the “Load Defaults” at the audio device setup, the DSD Playback Strategy will change to “convert to PCM”, I have to change it to “DSD over PCM” manually, to resume the native DSD playback.
Case closed, and thanks all for advice.