Steps to reproduce
Place a sticky piston pointe upwards one block above the ground
place a block of slime on top of the sticky piston
place another block of slime next to the other
place either a cauldron or a composter on top of that other slime block
place a redstone block underneath the second slime block so piston starts moving up and down
Now enter in the composter or the cauldron.
Observed results
Either it will glitch and you will be teleported down for a moment and you will be back in the cauldron, or you will be placed under it, or you will be ejected (it seems that you are ejected when you touch the corner in the cauldron/compost)
Expected results
That there is only one behavior, because the fact that it seems random makes it a bug.
Linked issues
Attachments
Comments 3

The different behaviors occur because the player may interact with different blocks during the sequence of movement. Sometimes they are inside the composter, sometimes touching the slime block, and sometimes inside the slime block. It depends on whether the blocks are extending or retracting when the player falls into the space.