Could be specular highlights or shader related, SMAA(1x) isn't going to be too effective against that type of aliasing unfortunately.
Downsampling together with SMAA works fairly well though but it needs a stronger GPU since the added resolution puts more strain on it.
SMAA as morphological AA doesn't just blur edges, it tries to find common shapes of aliased edges, calculates coverage of pixels and colorizes accordingly. But this only works if you have two evenly colored neighboring objects so you get a sharp zip zag line between them. Single pixel lines like this won't get smoothed by it because the morphological edge detection misses it entirely.