Split Shot does not deal headshot damage if both the primary bullet and a secondary bullet hit the same enemy.

[Termiinal]

It is understandable that split shots secondary bullets do not deal headshot damage, but at the moment if you are close enough to an enemy that both the primary bullet and a secondary bullet are hitting, the secondary bullet takes priority and deals the reduced damage. This does not seem to be the case with all guns, as Calico did not have this issue, but I believe this has to do with shotguns as testing on GT, Victor, and Doorman all had this bug occur.