Why does low poly appear fake shadows？

[206079409]

Hey guys,I recently found a problem, such as this model , although its surface is flat, it still has this fake shadow on low poly mesh.Does anyone know what could be causing this? If anyone knows the answer, I'd really appreciate it if you could tell me！THX GUYS！！！

[EGoddardJDP]

Does this issue persist when you render the model? it could just be the way the viewport is showing your smoothing groups.