Resource limit notifications are configured with some percentage value and Send Frequency is set to Once.
However, some customers receive the notifications every day.
Limit notifications configured to be sent Once will actually be sent out Once per billing period.
If usage percent does not change, notification may be sent several times during the billing period. PBA will stop sending notification for the current billing period only if usage percent changes. The fact that notification is sent more than once per billing period is a bug #PBA-58895.
Issue is planned to be fixed in future versions of PBA.