Issue with certain data and time as categories on Line Chart

Hi all,
    we're facing a problem with the population of a line chart: the issue is that if we have a date in Oracle such 2019-07-10 06:25:00 we can't see the point on the chart but it's filled with blank space. The problem is raised on every "25 minute" date stored on DB, I.E. 2019-07-10 00:25:00 or 2019-07-10 012:25:00 

- the date used for the chart are stored on a Oracle database
- as categories we're using the following code categories: todatetime(index(local!,"record_ts",null))  where record_ts is set as date on Oracle), is date_time in Appian

We solved the problem adding a second to the date (IE 2019-07-10 06:25:01): the behavior of the chart is correct, a point is viewed on the chart and the "lines" are correctly drawn between this point and the previous/following ones), but we're still wondering why we have this behavior. Anyone any idea?

Thanks in advanced

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