The bug

Slime balls sneezed by baby pandas can't be picked up by the player or hoppers.

How to reproduce

1. Run

   /fill ~-10 ~-1 ~10 ~10 ~-3 ~-10 air
   /fill ~-10 ~-1 ~10 ~10 ~-1 ~-10 hopper
   /setblock ~ ~3 ~ minecraft:repeating_command_block
   

   Put the following command into the command block

   /summon minecraft:panda ~ ~-1.8 ~ {HiddenGene: "weak", HandDropChances: [2.0f, 0.085f], PersistenceRequired: 0b, MainGene: "weak", Age: -56779}
   

2. Active the command block, stop it when there are 300 baby pandas.
3. Wait, till a baby panda sneezes a slime ball.
   → You and the hoppers can't pickup the slime ball(s)