When riding a horse upwards, such as when climbing hills, it almost always gets stuck in a weird position where the horse is seemingly in the ground, and the player can no longer move. I think this also happens with other animals when being pulled by leads, but I'm not sure if it's the same bug.
I tested this on my snapshot 24w20a server, and in a creative world with the same version. This was not a problem in the previous snapshot.
This is already tracked (and now fixed) in MC-272075