  While the international nEDM collaboration at the Paul Scherrer Institut
(PSI) took data in 2017 that covered a considerable fraction of the parameter
space of claimed potential signals of hypothetical neutron ($n$) to
mirror-neutron ($n'$) transitions, it could not test all claimed signal regions
at various mirror magnetic fields. Therefore, a new study of $n-n'$
oscillations using stored ultracold neutrons (UCNs)is underway at PSI,
considerably expanding the reach in parameter space of mirror magnetic fields
($B'$) and oscillation time constants ($\tau_{nn'}$). The new apparatus is
designed to test for the anomalous loss of stored ultracold neutrons as a
function of an applied magnetic field. The experiment is distinguished from its
predecessors by its very large storage vessel (1.47\,m$^3$), enhancing its
statistical sensitivity. In a test experiment in 2020 we have demonstrated the
capabilities of our apparatus. However, the full analysis of our recent data is
still pending. Based on already demonstrated performance, we will reach a
sensitivity to oscillation times $\tau_{nn'}/\sqrt{\cos(\beta)}$ well above
hundred seconds, with $\beta$ being the angle between $B'$ and the applied
magnetic field $B$. The scan of $B$ will allow the finding or the comprehensive
exclusion of potential signals reported in the analysis of previous experiments
and suggested to be consistent with neutron to mirror-neutron oscillations.
