  The Herbig Ae star HD 169142 is known to have a gaseous disk with a large
inner hole, and also a photometrically variable inner dust component in the
sub-au region. Following up our previous analysis, we further studied the
temporal evolution of inner dust around HD 169142, which may provide
information on the evolution from late-stage protoplanetary disks to debris
disks. We used near-infrared interferometric observations obtained with
VLTI/PIONIER to constrain the dust distribution at three epochs spanning six
years. We also studied the photometric variability of HD 169142 using our
optical-infrared observations and archival data. Our results indicate that a
dust ring at ~0.3 au formed at some time between 2013 and 2018, and then faded
(but did not completely disappear) by 2019. The short-term variability
resembles that observed in extreme debris disks, and is likely related to
short-lived dust of secondary origin, though variable shadowing from the inner
ring could be an alternative interpretation. If confirmed, this is the first
direct detection of secondary dust production inside a protoplanetary disk.
