Gravitational-wave observations reveal that the rate of merging black holes drops by ∼2 orders of magnitude from component masses ∼ 10 M_⊙ to ∼ 15 M_⊙. The increased compactness of the black hole progenitor cores may contribute to the ∼ 10 M_⊙ overdensity, but cannot fully explain the rate difference. In this paper, we consider the possibility that the overdensity is reinforced by supernova processes that result in efficient black hole formation from direct collapse in a narrow range around 10 M_⊙. We extend previous studies by considering a distinct subpopulation of failed-supernovae black holes, possibly separated by a gap in the primary mass distribution from the rest of the population. Using 153 observations from the latest GWTC-4.0 catalog, we confirm a strong peak in the primary mass distribution at 10 M_⊙, with a peak rate density of 7.36_(-3.11)^(+6.35) M_⊙⁻¹yr⁻¹ Gpc⁻³. The rate drops sharply and becomes consistent with zero at the 90 % level for primary mass m₁∈ (12.0, 16.1) M_⊙, then rises again to confidently nonzero values above ∼ 16 M_⊙ before falling at higher masses. Our results reveal structure in the mass distribution in the 10-20 M_⊙ range, with rate changes of multiple orders of magnitude across a few solar masses, consistent with a distinct population of failed-supernova black holes.