I'm trying to use the zabbix[host,agent,available] item via a zabbix proxy. It continually seems back a value of 2 (unknown)

All the other items running on this host are fine.

I've had problems trying to get this available item to work on other hosts via proxies, but after trying a bunch of different things (restarting agent/proxy multiple times, removing template, removing host) I've got it working in the past, but I don't seem to be able to do it this time, and to be honest I wasn't very happy with having to mess around so much to get it working anyway.