Using the Agent2 and the parameter "DenyKey" to filtering some ItemKey we will have on the Agent2 log an error like that:

item "Production server 11:system.boottime" became not supported: Unknown metric system.boottime 

Is not an issue but is a misleading message, in Zabbix there is no concept of "metric", usually we referring to "Item Key" all the concept of metric.

Also could be better to say that this "itemkey" is filtered by an ACL.

Thanks so much