Cats sometimes teleport to the player (MC-96369), sitting. If you try to make them get up, they often run to a nearby location and just stand there. After that, telling them to sit doesn't work, even if you reload the world, restart the game, et cetera. The only way to get them to sit is to break the block under them, and then they will sit. Some really odd things can happen if they see a chest or bed they can't get to.