when standing on a slime block with a piston under it the player is not launched into the air. if you stand on the edge of the slime block it seems to work more often but when the launcher is surrounded by blocks or you need to fit into a 1x1 hole above, you cannot stand on the side. occasionally the piston action pushes the player sideways one block instead of shooting upwards as intended. i stopped playing my realms over a month ago due to this glitch and just recently tried again but the issue persists.