What is this shadow in URP

This shadow in the URP scene is driving me crazy. Default scene with added plane (have tried other objects) - This shadow appears in the corner of your screen if camera is oriented at this location. Shadows follow camera along the axis it is pointing (i.e. shadow moves), but if you try to look at it, the shadow disappears.

Have tried disabling all objects except for the plane, shadow is still there. If you go into lighting settings and disable shadows it disappears. So confused about what is casting it...