Lighting Issue

Has anyone seen this / know the cause of this?

Single Point light with lighting baked. However only half the light appears, split horizontally, then as you move closer the bottom half fills in. I would like to remove this artefact but do not know the cause of it.

The 2 SS images are side by side, sorry should have left a gap.

This could be to do with your light maps. That back wall should be one UV island with no breaks.

Sadly UV is a single island, Light map is also a single island.