There are local servers all around the world. You generally interact with the one closest to you, but it isn’t the “single source of truth.” At some point changes should be reconciled with the source authority, but all the remote servers are trying to update the source at pretty much the same time. Resolving updates from your global diaspora of servers in an accurate manner is hard and you’re likely to see odd bugs arise, especially when a large number of people take similar actions at once. You can see this in trending viral video likes–toggling your like on and off or viewing the video at the same time from 2 different locations is likely to give you a different like count each time. You can also see this when Trump rebrands the official POTUS account and starts spewing his vitriol through it, large numbers of people will realize they don’t want to deal with his bull shit, and some of their updates will fail to resolve in a timely manner.

This doesn’t happen to everyone, but if you unfollow someone and it works you aren’t gonna complain.