  During their formation phase stars gain most of their mass in violent
episodic accretion events, such as observed in FU Orionis (FUor) and EXor
stars. V346 Normae is a well-studied FUor that underwent a strong outburst
beginning in $\sim1980$. Here, we report photometric and spectroscopic
observations which show that the visual/near-infrared brightness has decreased
dramatically between the 1990s and 2010 (${\Delta}R\approx10.9^{\rm m}$,
${\Delta}J\approx7.8^{\rm m}$, ${\Delta}K\approx5.8^{\rm m}$). The spectral
properties of this fading event cannot be explained with variable extinction
alone, but indicate a drop in accretion rate by 2-3 orders of magnitude,
marking the first time that a member of the FUor class has been observed to
switch to a very low accretion phase. Remarkably, in the last few years
(2011-2015) V346 Nor has brightened again at all near-infrared wavelengths,
indicating the onset of a new outburst event. The observed behaviour might be
consistent with the clustered luminosity bursts that have been predicted by
recent gravitational instability and fragmentation models for the early stages
of protostellar evolution. Given V346 Nor's unique characteristics (concerning
outburst duration, repetition frequency, and spectroscopic diagnostics), our
results also highlight the need for revisiting the FUor/EXor classification
scheme.
