https://gyazo.com/3a274e376ffca8560a5bda9d842a0d86
https://paste.dimdev.org/jeyepesubo.mccrash
I just placed down a spawner, got a syringe with fluid cow, placed it in, and crashed.

Server crashes when an unsupported mob type is placed in a spawner.
See crash report https://pastebin.com/ZD5bnSGt.