When a mob is killed by lava placed directly on top of hoppers, some of its common drops do not make it into the hoppers. Presumably, they are destroyed by the lava before the hoppers can suck them.

Steps to reproduce:
1. Build the construction shown in the video clip. There are 9 hoppers under the lava whose funnels all direct their contents into the visible hopper behind the chest.
2. Summon a mob that has multiple common drops above the lava.
3. After the mob burns up, examine the contents of the chest. Notice that no matter how many times you repeat the experiment, you never get more than one type of item dropped.

In the case of an iron golem, you may get either a poppy(ies) or iron ingots, but not both. You should always get iron ingots.

In the case of a cow, you may get either cooked beef or leather, but not both. You should always get cooked beef.

This report relates to, but is not a duplicate of, MCPE-21164.