Most of the updates for Pokemon Go recently have been usually made for the buddy system. The updates of the game might make the Pokemon rare nest locations to change. This is an important update for trainers who are working on evolving certain Pokemons. According to Otakukart, it was noted that the nest locations are an important part of Pokemon Go. Nest locations of Pokemon Go can help players to make good evolutions such as Gyarados. The update can be expected to change the locations of these nests anytime soon. It is however not an absolutely negative change, but it is just made for exploration purposes that the game likes for the fans to experience.
As cited by the Bitbag from Reddit, fans are saying that the change might occur within three to four days. It is needed that fans, who have already memorized the current locations for specific creatures, should look at some other places. Similar to Pokemon Go's previous updates, some Pokemons are not guaranteed to appear for quite some time. It is suggested that Pokemon trainers should go to Pokemon rare nest locations before the update will come. This might help them find Eevee while they still can. Fans who would like for their Magikarp to evolve should already start to go to the nests, so that they can evolve before the update takes effect. The Pokemon buddy system can also help with the evolution.
Bitbag added that changes in the Pokemon Go rare nests are not just about switching of Pokemon area. It will also replace other Pokemons. For example, Poliwag's nest might be replaced with Abra one or Abra one might be replaced with Poliwag. However, it doesn't mean also that the Pokemon will disappear permanently. It only means that some nests might disappear for an indefinite time.