The bug
Shulker bullet take damage from any source and can be moved by fishing rods with the Invulnerable
NBT tag.
How to reproduce
Run
/summon shulker_bullet ~ ~1 ~ {NoGravity:1b,Invulnerable:1b}
Punch the shulker bullet in survival
→ ❌ The shulker bullet die
Video demonstrating the issue: https://youtu.be/Gqhddi_2ym4
Can confirm in 20w51a.