What caused this mysterious stellar occultation on July 10, 2017 from something ~100 km away from 486958 Arrokoth?
There were three attempts to measure Arrokoth by occultation, and the June 3rd attempt didn't detect anything.  The July 10th attempt had a tiny blip, that appeared to be in the &quot;wrong place&quot;, well away from the location that astrometry had predicted. The July 17th occultation was successful, it determined the shape and location well.
Some thought that the July 10th &quot;blip&quot; might have been evidence of a moon.
It was not, it turned out that there was an error in the software that was used to produce the astronometry (the author of the software describes one as &quot;a case of me failing to read my own documentation, another one a sign error&quot;) If those bugs are fixed, then the blip on July 10th is moved to the same place as the blips on July 17th.  That blip is Arrokoth.