[Bug Report] Mobs not Spawning from Spawners

Minecraft Username: chargers2417

Brief Description: Mobs (Skeleton in particular) not spawning from spawner.

Instructions: Set up a spawner and wait for mobs to spawn. (Picture of set up below)

How many times did you recreate this bug?: Roughly 10, all 10 times they didn't spawn.

Result: The flame particle that the spawner gives off when mobs spawns goes off but no mobs appear.

Expected Result: Mobs to spawn.

Evidence:

 

Still happening, flame particles are there but no mobs.

 

Nvm, I was in the main world. Please ignore my failure at reading.

._.