A big one is that the SM straight up does not account for neutrino mass, which we know they must have due to oscillations in flavor from sources such as the Sun

A big one is that the SM straight up does not account for neutrino mass, which we know they must have due to oscillations in flavor from sources such as the Sun. [1] [1] https://en.wikipedia.org/wiki/Solar_neutrino_problem https://en.wikipedia.org/wiki/Solar_neutrino_problem OOPS: I see a sibling comment also covers this. Oh well, I'll keep this one up since it's slightly more eye-catching.