Deathslinger's harpoon doesn't damage when applying Forced Penance and the survivor is healthy
As Peanits said in this thread:
"Being healthy while broken should not be possible".
As he explained, that is why survivors become injured when reaching full infection with Plague, because the Broken status effect is applied, and not because of the infection itself.
When shooting someone healthy at distance, and there's another injured survivor closeby, the Broken status effect is applied, but the survivor doesn't become injured, so it's a bug.