Overlapping Columns In Highchart

Hello fellow App Builders,

I get overlapping columns in a column chart in Apps:

The sql query looks like this:
SELECT AVG(po_to_confirmation_time) as avg_po_to_ab, {{variable_timeAggregation.sql}} as group_col FROM inputTable i GROUP BY group_col ORDER BY group_col DESC LIMIT {{variable_timeAggregation.limit}}

Does anyone know why the columns overlap?

Thank you in advance for any hints