  We report on three optically bright, ~15th mag, point-sources within 10
arcsec of each other that vanished within 1 hour, based on two consecutive
exposures at Palomar Observatory on 1952 July 19 (POSS I Red and Blue). The
three point-sources have continued to be absent in telescope exposures during
71 years with detection thresholds of ~21st mag. We obtained two deep exposures
with the 10.4-m Gran Telescopio Canarias on 25 and 27 April 2023 in r and
g-band, both reaching magnitude 25.5 (3-sigma). The three point-sources are
still absent, implying they have dimmed by more than 10 magnitudes within an
hour. When bright in 1952, the most isolated transient source has a profile
nearly the same as comparison stars, implying the sources are sub-arcsec in
angular size and they exhibit no elongation due to movement. This triple
transient has observed properties similar to other cases where groups of
transients ("multiple transients") have appeared and vanished in a small region
within a plate exposure. The explanation for these three transients and the
previously reported cases remains unclear. Models involving background objects
that are optically luminous for less than one hour coupled with foreground
gravitational lensing seem plausible. If so, a significant population of
massive objects with structure serving as the lenses, to produce three images,
are required to explain the hundreds of sub-hour transients.
