  Topological superconductivity is expected to spur Majorana zero modes --
exotic states that are also considered a quantum technology asset. Fractional
Josephson effect is their manifestation in electronic transport measurements,
often under microwave irradiation. A fraction of induced resonances, known as
Shapiro steps, should vanish, in a pattern that signifies the presence of
Majorana modes. Here we report patterns of Shapiro steps expected in
topological Josephson junctions, such as the missing first Shapiro step, or
several missing odd-order steps. But our junctions, which are InAs quantum
wells with Al contacts, are studied near zero magnetic field, meaning that they
are not in the topological regime. We also observe other patterns such as
missing even steps and several missing steps in a row, not relevant to
topological superconductivity. Potentially responsible for our observations is
rounding of not fully developed steps superimposed on non-monotonic resistance
versus voltage curves, but several origins may be at play. Our results
demonstrate that any single pattern, even striking, cannot uniquely identify
topological superconductivity, and a multifactor approach is necessary to
unambiguously establish this important phenomenon.
