Hi, as subject.
Is it a normal situation or bug issue for matomo?
This shouldn't happen. Where exactly do you see this behaviour?
It is real case!, our matomo has happened. our matomo is version 3.5.1.
In the 2019-04-05 collection data that we use the API to export, there are three data for 2019-04-06 00:00:00, and the 2019-04-06 data collected by the export API also has the same three pieces of 2019-04-06 00:00:00 data.
Which export API do you use exactly? If you use the Live API we may return the data for two days when requesting one day AFAIK. This may be on purpose.
Also I recommend you update to the latest version to see if it is fixed. Otherwise we can't really look into it.