random desync that even happens in singleplayer
That's quite an achievement. First time I've heard of singleplayer desync. How did they even manage to do that?
One assumption is that it's trying to gen/load up chunks offscreen; Let's just say that the terrain generation isn't that well optimized, to the point that you can outrun terrain gen and get frozen in the air by jumping into ungenned chunks on mid-spec machines.
Mobs will happily attack you while you're stuck that way, tho, but you can jump out.
The weirdest thing is, you'd expect that to be processor lag, as the game hangs and loads the level, but no, players, NPCs and mobs do their own thing, no frame drops, next to this gaping rectangular chasm of unreality.
Except when they don't. So I don't even.
Edit: Admittedly, I'm pretty sure this did happen in Terraria too, but that was serverside exclusively iirc. I do remember this one time where I was happily hopping through what was thin air on my screen and constantly clipping through this one Blood crawler that, on another player's screen, was still chasing us down, utterly creeping him out.
And the issues with worm heads not dying on some players' clients, fighting them after the things had been killed.
So that game also had its fair share of problems, some of which might have been inherited.