Put the summary of the bug you're having here

What I expected to happen was...:
A machine made to bounce the player from within the air. Normally, (as in 1.13) this would launch the player to the side.

What actually happened was...:
The slime block merely pushes the player as if it were any normal block (ie stone)

Steps to Reproduce:
1. I built a simple machine to launch the player upward to consistently get the player into the air
2. step onto the bottom slime block
3. before launching (with the button) hold shift until you are sure you are not jumping
4. Let go of shift
5. press button and do nothing