I've been noticing Lox seem...delayed? I guess? They do show up in my game but so far i have arrived to a plains to find lox already there about twice since i started playing again (in both cases, absolutely massive plains biomes so its possible they spawned while i as exploring and just happened to already be there by the time i looked their direction). The rest of the time when i find them Im hanging out nearby a plains doing something like building and turn around to find a herd that wasnt there a second ago uncomfortably close to the framework of the base im trying to lay out.
They don't seem to have blocked spawns though. I had found one of those "islands" where it's basically just a single rock sticking out of the water, but it counted as plains so i decided THAT was going to be my plains farm island. Was leveling everything out and expanding the actual landmass of the island when i took my workbench down to move it closer to the other side i wanted to work on and in just that moment the workbench was down, boom, sudden lox on my tiny rock, me: "now wait a minute, let's talk ab-*splat*" so uh, that went well lol. Of course since this was just a tiny rock i was actively trying to make buildable at the time, no portal or anything set up there yet to return with either (because i figured the workbench had me covered, was not expecting death to spawn in the 5 steps it took me to replace the bench, lesson learned).