Dark shading on uploaded model

With a recent upload, a section of my upload has shown up darker than the rest. It is an old truck and it is the rear fenders (See photos attached.) I have tried a few things like flipping the normals, checking the normal direction etc, but have had no luck. If you have any suggestions of what to try, I would greatly appreciate it. Everything seemed fine when exporting from Blender and into substance painter, but am now having this issue in sketchfab, so I am not sure what is causing it. Any help would be appreciated!

Here are photos of it in both Blender and Substance, where things worked fine.

My first guess would be to check you don’t have any vertex colours being uploaded, since I know Substance uses these for various masking functions.

To do this on Sketchfab, go to the ‘Scene’ tab and disable them there.

Thank you for your reply! I don’t believe that any vertex colors loaded in, as I don’t see the option to disable them under the scene tab. However, upon playing with some of the processing filters, the subsurface cleared up the dark areas, to a normal appearance. I have rolled with this setup for now, but perhaps this is a lead to what may be causing the issue?

perhaps its related to custom split normals which you would need to clear in blender