The mod ice and fire is trying to access resources which are only available on the client and not on the server: https://mclo.gs/slDuie7#L3215
You should report this to the creator of the ice and fire mod
The creator of the mod gave me an answer, apparently I need to: remove registration of NULL owner ID in EntityDragonEgg:registerData(). I'm not quite sure where I have to do this at though.