In our custom Data Feeds (CDF), we observed that for some days the day_string and event_time and day_string are not in sync

• Audience Manager
• Data Feeds
• CDF
• Reporting 

Event_time is the time the call is made to Distributed Call Signaling (DCS) and day_string is the day we show in the CDF bucket, as we do not expose the information inside the actual CDF files. This represents the date when the internal AAM back end generates the data, so if it happens to run a little later than the actual event, those two fields can be out of sync.

As per the above, the same is expected and working as designed.