I have a zabbix setup that uses LLD. The LLD key is a trapper.
I use some python I wrote with the zbxsend.py libary to send the JSON that creates the discovery itmes.
In Zabbix 2.4 this works fine. The zabbix-server processes the trapper data and the LLD all works correctly.
In Zabbix 3.0 This does not work. The processing fails. The trapper receives the data (I ran with debug=5) but fails to process it.
I've since downgraded back to 2.4
I don't currently have logs as the VM's have been pulped but if need be I can recreate the whole setup again.