  Observed changes in protostellar brightness can be complicated to interpret.
In our JCMT~Transient monitoring survey, we discovered that a young binary
protostar, HOPS 373, is undergoing a modest $30\%$ brightness increase at 850
$\mu$m, caused by a factor of 1.8$-$3.3 enhancement in the accretion rate. The
initial burst occurred over a few months, with a sharp rise and then shallower
decay. A second rise occurred soon after the decay, and the source is still
bright one year later. The mid-IR emission, the small-scale CO outflow mapped
with ALMA, and the location of variable maser emission indicate that the
variability is associated with the SW component. The near-infrared and NEOWISE
$W1$ and $W2$ emission is located along the blueshifted CO outflow, spatially
offset by $\sim3$ to $4^{\prime\prime}$ from the SW component. The $K$-band
emission imaged by UKIRT shows a compact H$_2$ emission source at the edge of
the outflow, with a tail tracing the outflow back to the source. The $W1$
emission, likely dominated by scattered light, brightens by 0.7 mag, consistent
with expectations based on the sub-mm lightcurve. The signal of continuum
variability in $K$-band and $W2$ is masked by stable H$_2$ emission, as seen in
our Gemini/GNIRS spectrum, and perhaps by CO emission. These differences in
emission sources complicate infrared searches for variability of the youngest
protostars.
