[Grey Card and RGB Values]

So I should include the grey card and adjust exposure in AP to 55,55,55? 

I can live with that, but I suspect I won't be the last one tripped up by this major variance from CR/LR.

[Grey Card and RGB Values]

I understand those explanations but they don't apply to the actual problem.  The comparative image I posted is of AP with the image assistant turned on.  Both Camera Raw and AP Develop report the card as 128,128,128 (or so) but the AP image is much too light.  If I include a grey card in a photograph then adjust the exposure in AP so it samples at 128,128,128 I don't think I'm going to like the result.  Still assuming I'm doing something wrong.

Windows 7, Canon S120, AP  1.6.4.104, Camera Raw 9.1.1

[Grey Card and RGB Values]

I expected the values to be around 128 because that's what the card image measures in Camera Raw.  The AF image is visually much lighter than medium grey, the sampler from Photoshop measures it at about 180, 180, 180. I assume I've done something wrong in Affinity.

[Grey Card and RGB Values]

I should preface by saying I'm new to both Affinity and camera raw processing.

I take a photo of a standard grey card as raw (.cr2) and open in Develop (Assistant turned off). The onscreen image is medium grey.

I set a sampler point in the card, the rgb values are 55,55,53.  Why aren't they all 128 (or so)?

If I enable the Assistant (and the tone curve) the rgb values are all around 120, but the image is much lighter than the grey card. 

[Highlight clipping indicator photo persona]

As a new user, +1 for incorporating the Alt-drag clipping indicators in Curves for the Master and color channels.  It's a very basic part of my workflow.