You mean the way the H in Honolulu has some missing ink, but the H in Hospital doesn’t? I would think a bad spot in the ribbon could do that, or maybe just a key that wasn’t pressed completely.
Digital scan of an uneven image; result is not unusual.
A lot of people are sounding stupid today as they try to sound smart.
Irregularity in the texture of the paper, the typewriter ribbon, the fold of the typewriter ribbon, the amount of ink that was on the typewriter ribbon, the amount of dust or small-paper-bits residue that was on the original piece of paper, the amount of pressure applied by the typist striking the typewriter key, the speed at which the typewriter key was struck, or some combination of the above.