Why are you using HDRI-Optimized output? I'm pretty sure that BB's test renders did not use that, could make a difference. If you export your image as HDRI then the colorspace is much bigger, and linear as well. According to the manual, this only should be switched on when you plan to use the images in .hdr or .exf formant.

Maybe the difference is here?

 And, pretty please, check if the gamma value in the textures is 1.0 as well. If you switch global gamma correction on the images files may still have an different value. If the texure was loaded with a different GC value and global GC was set to 1 you will still get a different result from switched off GC, because the image file is GC-corrected when incomin - just not when outgoing.

 

A ship in port is safe; but that is not what ships are built for.
Sail out to sea and do new things.
-"Amazing Grace" Hopper

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