When using a spawn egg to place any neutral mob that can be angered into a Spawner block, the mobs will not show up and the logs will spammed at an insane rate that will eat up memory at an uncontrollable rate.

For the picture below, the Spawners were run for only about 10 seconds and it produced this 8MB log file filled to the brim with errors: latest.log

Imagining this running for a full minute or more as players are playing with these spawners (which will still spawn the mobs), they will start accumulating a log file that could reach a hundred MB. And if they spend quite a while in the world with tons of these spawners, the log could easily hit a full GB in size. 

This report is based on this marked invalid report except this time, the issue was reproduced in vanilla. For whichever developer assigned to fix this bug, please check out the original report below as Draylar has found the exact line of code that is causing the issue:
https://bugs.mojang.com/browse/MC-192362?jql=project%20%3D%20MC

Here is a picture of the bug below. Leftmost is regular default spawner. Then: