Hi @Heqixin! I agree with @rbs_sci that this looks like duplicate particles. Gold-standard FSC (GSFSC) filtering relies on the assumption that the particles in each half-set are distinct, but if there are duplicate particles it’s possible for the same particle to end up in each half-set (since there are multiple images of that particle).
If you run the particles through a Remove Duplicate Particles job and then reconstruct them, does the FSC look more believable?