I've noticed it first on #Gab instances (I remember this being a thing back in the olden days of #GabFed) and #SoapBox, and IIRC a few #Mastodon instances have it too.
@realcaseyrollins Well my first guess was the instances were doing it for clout (to seem more active than they actually are), but I doubt @alex would have anything like that installed, so it's almost certainly just some ancient glitch.