@GoldenHelmet It seems that it picks you up when you are facing south and hugging the side of it.
I haven’t been able to recreate this but the shulker box lifted me up even though I was not on it. I think that there may be a desync with the player collision box and the world around it. I have also experienced random suffocation by blocks and random swim noises by water.
@Jay Wells It was in a local world.