Hello,
This behavior is expected. Since /Game/Artist/Sternyang/Material/Translucency is a translucent material and doesn’t receive shadows by default, the wall won’t be able to occlude the light specular reflection generated by the PBR lighting model. Opaque materials will receive shadows normally and thus don’t have the same problem.
To get shadows on translucent surfaces, please check this documentation page for guidance: https://dev.epicgames.com/documentation/en-us/unreal-engine/lit-translucency-in-unreal-engine
Please let us know if this helps.