Alert Notification Framework: Emails Not Generating Multiple Times

We're using PeopleSoft HCM 9.1, Tools 8.51.10. I've set up alerts under Enterprise Components > Events & Notifications > Notifications Framework, as well as the setup under the "Alerts" sub-menu.

When I run the alerts  scheduled for every half hour, the email generates once but not subsequent times. Frequency set to "1" hour. The subsequent transactions are listed in Enterprise Components > Events & Notifications > Notifications Framework > Notification Details. I also see rows written to EOEN_EMLNTFY, just not with email addresses on all rows (only the first set). And, no subsequent emails get sent after the first one that was received. Any ideas what could be missing? I'm using system-level overrides to set specific email addresses, but I shouldn't think that should matter.