I noticed a weird smallish but prominent spot on two places on one of my models thinking it was caused by me I went to check the textures and found it was not. I then discovered it was been caused by the environment lighting.
I know you are using the hdrlabs stuff but now I am wondering if you are using a dual environment setup? The sIBL collection includes a blurred low-res version of the environment to use for diffuse lighting calculations and the hi-res normal version is only used for reflections.
I presume this spot is been caused due to using the hi-res ( or non blurred ) env map for diffuse influence? If not Im interested to know what is causing this artifact.
In blender cycles this is the node set up for environment lighting using two maps as explained above :