Lightmaps ios square artifacts

Yet another lightmap question. Can anyone give me some advice. My lightmaps in iOS are producing a strange square looking artifact in one section of my model. Has anyone seen this before? This is really my first attempt at lighting so I am not sure if I am doing something fundamentally wrong.

I have attached my lightmap settings and a picture of the artifacts that are showing up. Any help is greatly appreciated.

Anyone? Lightmaps in Unity are kinda like playing the lottery at this point. Has anyone seen this before? Just wanna at least get some advice on something to try. I feel like I have ticked all the lightmap boxes and adjusted all the sliders to no acceptable results.