In my own experience I've seen a little brightness variance up or down when I do a calibration but maybe up to 15nits or so. One thing to keep in mind is that your peak brightness will be impacted by how warm the screen is. It gets a little brighter after warming up and / or if the brightness window pattern is up longer. Is there a chance your set wasn't on as long with the lower measurement?I'm beginning to think that my 65" C9 has 'pre-mature aging' mostly due to 5 of the big compensation cycles being run @ only 1600hrs SOT, partly due to my inexperience when first getting it...
Currently my max peak brightness in HDR is ~680 nits and DolbyVision is slightly higher... However when I first got into the calibration scene 2 months ago I remember measuring ~710 nits.
Throughout the two months I had to manually run two of the big compensation cycles as my panel developed strange horizontal lines running along the centre of the screen - fortunately the comp cycles fixed it, but now I'm concerned it's decreased the brightness of my display which I'm not happy about.
I'm hoping to hear of some other people's perspectives as to whether I should be concerned, whether this is an acceptable brightness reading and whether there is anything I can do to improve it.
P.S I've been sure NOT to decrease the red channel during the SM WB calibration which from what I've read can result in reduced peak brightness.
Thanks for your time.