May 21, 2019 Update: The Red Dead Online dead horse bug that we describe below has now been fixed.

Red Dead Online is beset by dead horses.
Since the major update last week catapulted the game out of beta and into full release, adding a large selection of new content and features, players have begun to encounter creepy piles of horse corpses in the game.
This is definitely up there as one of the most disturbing and creepy bugs in a game, ever. In random locations in Red Dead Online's game world, usually at road intersections, massive piles of dead horses are spawning, numbering in the dozens. It's certainly shocking to see when you first encounter the phenomenon, not knowing to expect it.
Being so odd had players suspecting it was more than a bug. The eerie appearance of these piles of dead horses had some players speculating that this may even be intentional, a tease regarding future Red Dead Online content in the vein of Undead Nightmare, a DLC expansion for Red Dead Redemption.
Rockstar has since clarified that this is in fact, merely a bug and not an intended content tease. While somewhat disappointing, we really don't think Rockstar would bring back Undead Nightmare for Red Dead Online so soon after full launch.
The bug is being investigated by Rockstar and should be fixed sometime soon. In the meantime, these pile-ups may yet manifest in your game. So far, the bug does not seem to affect singleplayer. Whether it just hasn't been reported yet, or Red Dead Redemption 2 is really immune to dead-horseitis is currently unknown.
Dead horse mounds aren't the only bug introduced by this latest major update. Red Dead Online has been suffering frequent crashes that have yet to be fixed, and unfortunately, legal issues prevent the poker mini-game from being available in every country. Hopefully, the horses and crashes will be fixed, even if Rockstar can't do anything about the poker.