There are random failures in the agent/server when it comes to the keys in items that will result in an items showing as "not supported" The item IS supported, because in some cases it was working previously, but in all cases it's from a template that works fine on other like servers. thus far I have seen this failure with system.cpu.util and net.if.in
Once an item decides it is not supported, it will never work again. enabling the item does nothing as it returns to not supported on the next check. this renders zabbix completely useless to monitor that item.