Forge version: 1.12.2-14.23.1.2560
Twilight Forest version: (this is the build number)3.5.263
Link to crash log: (please use a paste site such as gist, do not attach the .txt or paste the log inline)

Steps to reproduce:

1. go into gamemode c
2. place spawner
3. put firefly spawn egg in spawner

What I expected to happen:

Spawn fireflys in world

What happened instead:

nothing the firefly spins round and round in the spawner but never spawns

Thank you guys for reviving this great mod and for all your hard work.
Happy Holidays

Is the spawner in the right conditions (large enough space to spawn them, dark enough so the spawner isn't disabled)?

The attempts to spawn the mob by spawner must be below sea level and dark