Weird light on movable objects

I’m having problems dealing with that light in the red circle in the pic below. The door is a BP door (movable), the right part of the door is a static. (green part is movable, yellow part is static in the pic.)

The directional light in the scene is stationary, the skylight is static. No other lights exist in this level.

I can remove that weird light by selecting “force surface” to be the lightmap type in the mesh’s lighting panel, as the pic below. But I think this is only a temporary solution, and I still want to know where this light comes from and what causes this problem.