Faint nebulae or clusters. But there are many faint galaxies not listed in those catalogs. In addition, the magnitude estimation of nebulae and clusters by the PIXY system tends to become fainter than that of normal stars. So they may be judged as catalog errors more.
Some stars become several magnitude fainter than the value recorded in star catalog.
Since faint nebulae and clusters always appear fainter than recorded in star catalog, they are always output as candidates of catalog errors by the PIXY system. In principle, when an object was not detected at all during five or more nights but exists as a very faint object actually, much fainter than recorded in star catalog, it will be registered as MisF object. It is very faint and cometary, so it should be a galaxy. ID R.A. Decl. Dr. Arne Henden also pointed out that the R.A. and Decl. should be recorded in the list.