I am having this same issue. I'm on Server 2008, running Logicity 1.8.9.0. My rrd runs fine, manually. It runs on its schedule, if I am logged in. It does not run when I am not logged in.
The task is enabled, is set to run with highest privileges, and the password is saved. The user running the task is a local admin. I'm using a UNC path to my file.
The job history in task scheduler looks like the job runs, but the emails never get sent. We had IT look at any & all permissions or other things they might identify, to no avail.
At this point my workaround is to keep myself logged in, but this is impractical in the long term. Has anyone had this issue & been able to resolve it?