18w46a abnormal piston

i have built a kelp farm that followed ilmango's methods (link: https://www.youtube.com/watch?v=maMnF9CbbTY&t=643s), the fly machine works fine along 1.13 to 18w45a. However, the updated snapshot yesterday creates something wrong i don't know yet on the piston, it makes the piston frequently pushes and contracts with no reason. And eventually, lags crush my game.