  A semiconducting nanowire fully wrapped by a superconducting shell has been
proposed as a platform for obtaining Majorana modes at small magnetic fields.
In this study, we demonstrate that the appearance of subgap states in such
structures is actually governed by the junction region in tunneling
spectroscopy measurements, and not the full-shell nanowire itself. Short
tunneling regions never show subgap states, whereas longer junctions always do.
This can be understood in terms of quantum dots forming in the junction and
hosting Andreev levels in the Yu-Shiba-Rusinov regime. The intricate magnetic
field dependence of the Andreev levels, through both the Zeeman and
Little-Parks effects, may result in robust zero-bias peaks, features that could
be easily misinterpreted as originating from Majorana zero modes, but are
unrelated to topological superconductivity.
