Was this possibly related to scheduled reports? We do have an issue where scheduled reports if based on custom reports would not have any data. We do have a fix for this in 7.5.2 which is currently in limited support.
•Corrects the database query for scheduled report generation to address a problem where a scheduled report based on one of the built in favorite reports would always show no data.
(Low severity. Reference: KB78848.)
if you contact support and request it for this issue this might help.