There is a bug with Structure Block that upon loading the saved structure will keep spawning saved entities.
Steps to Reproduce:
[Step 1] Save a structure that includes entities. Settings: Include Entities - Include.
[Step 2] Load that structure with settings:
Include Entities - Include
Remove Blocks - Remove
Animation Mode - Place by Layer or Place by Block
Animation Time - any number greater than 0.
The structure block will keep rapidly spawning the saved entities and cannot be stopped.
The structure block should spawn only one entity for every entity in the saved structure.
Picture 1 shows the saved structure.
Picture 2 shows the expected result.
Picture 3 shows the current result.
The bug spawns so many entities that the world will immediately start to lag and the lag will worsen over time.