  We report high-precision mass measurements of $^{50-55}$Sc isotopes performed
at the LEBIT facility at NSCL and at the TITAN facility at TRIUMF. Our results
provide a substantial reduction of their uncertainties and indicate significant
deviations, up to 0.7 MeV, from the previously recommended mass values for
$^{53-55}$Sc. The results of this work provide an important update to the
description of emerging closed-shell phenomena at neutron numbers $N=32$ and
$N=34$ above proton-magic $Z=20$. In particular, they finally enable a complete
and precise characterization of the trends in ground state binding energies
along the $N=32$ isotone, confirming that the empirical neutron shell gap
energies peak at the doubly-magic $^{52}$Ca. Moreover, our data, combined with
other recent measurements, does not support the existence of closed neutron
shell in $^{55}$Sc at $N=34$. The results were compared to predictions from
both \emph{ab initio} and phenomenological nuclear theories, which all had
success describing $N=32$ neutron shell gap energies but were highly disparate
in the description of the $N=34$ isotone.
