Pokemon Go seems to have a disappearing Shiny Pokemon problem. Late last night, a post on /r/TheSilphRoad, the largest Pokemon Go community on the Internet, presented strong evidence that the Shiny version of Taillow has been missing from the game since the end of the Lunar New Year event back in February. The post detailed how multiple large Discord groups had found no evidence of any player finding a Shiny Taillow either locally or on social media since mid-February. While there was a chance that the large group of players simply had the worst luck possible, it seemed more likely that Niantic had somehow disabled Shiny Taillow when they ended the Lunar New Year event.
Hours after the post went up, Pokemon Go players reported finding Shiny Taillow in the wild once again, likely because Niantic (who follows /r/TheSilphRoad) had seen the post and quickly rectified their error. However, this isn't the first time that something like this has happened - ComicBook.com reported on similar incidents that affected the Shiny versions of Krabby and Magnemite earlier this year. The Shiny Pokemon seem to get disabled shortly after an event, either due to Niantic reverting Pokemon Go's settings back to a default that didn't include these Shiny Pokemon or because of some other error.
So, why is this a big deal? Well, Shiny Pokemon are one of the main reasons that players keep logging into Pokemon Go after they've filled their PokeDex and reached Level 40. They're extremely rare under normal circumstances (Pokemon have about a 1 in 450 chance of being Shiny) and are seen as a bit of an accomplishment when players finally get their hands on one. Disabling a Shiny Pokemon species without telling the player base means that players looking for a Shiny Pokemon could waste a lot of time trying to find something that's not there.
Hopefully, this issue gets rectified and Niantic puts a system in place to prevent these sort of incidents from occurring. The comment sections on /r/TheSilphRoad aren't too friendly at the moment, and these sorts of unforced errors is how players decide to quit a game for good.