The pin is a friction fit in the hammer holes and the disconnector should be loose on it (if I remember correctly).
You'd think the pin would be the "right size" if it would drive into the hammer (not too big in diameter) and if it stayed in place then it couldn't be too small in diameter.
Hard to believe someone didn't notice it when they put the assembly together but maybe there is no "test/inspection" required for that step of assembly.
Or, the hammer "ears" where the disconnector sits might me slightly squeezed together and pinching the disconnector.
Any way it goes, it ain't right and needed to be corrected. Your trigger pull/reset/operation should be smoother from now on.