Hi Daniel .
I’ve taken the liberty to take a look at your draft model (to which I have access as Sketchfab staff), and opened the .obj file you uploaded in Blender.
It seems like the original model has the flaw you mention (see screenshot below).
Depending on the original software you used to create your model, my guess would be that you have somewhere a transform being applied to your UVs (look for parameters called “UV scale”, “UV transforms” or “UV offsets”), which does not export correctly to obj.
You could try to “apply” those values, so that for instead instead of a scale of 0.98, your software sees a scale of 1.0, then re-export the model.
Otherwise, and if you have the capability to do so in your editor, could you try to upload the same model with a .fbx format ?
If you don’t manage to solve this issue with the info above, could you tell me which software you are using?
Good luck !