I was fighting the Heart of Ender and I died during the fight, I had 2 lives left and when I came back using the piston I was stuck mid-air and unable to move at all. I was able to use my weapons and artefacts.

Steps to recreate:

1.Die at the second stage of the final boss (Heart of Ender).

2. Go back using the piston.

This only happened to me once but I had to restart the entire level because I could not move or hit the boss.