There is an annoying behavior of Zabbix with LLD. When a resource is not discovered anymore, if it was related to a trigger in PROBLEM state, the trigger never comes back to OK state. The trigger stays in PROBLEM even after the "Keep lost resources period". As there is no way to manually reset or clear a trigger created by a LLD rule, we have to unlink and clear the template and link it again to make the trigger disappear. For example, we have database state triggers that still fill the dashboard whereas they we deleted monthes ago.
This can be very problematic for "software" resources discovered with LLD (databases, filesystems, virtual servers, etc), as they are more likely to be removed when a problem occurs.