Lighting throws a shadow instead of a light, while lighting opposite side of the model

I have the weirdest bug. My lights behave precicely opposite than they should. They cast a shadow on the side that is ment to be lit! As if they are lighting using a shadow and not light?

Any advice? Thank you very much in advance.

Update and SOLVED! I went back to Blender, deleted all “actions” (blenders feature related to animation) , then re-exported the model. Now it works. It seams that when exports have more than one “action” , the lighting on Sketchfab seams to be messed up/reversed.