Hello Leif,
Is your data stored in a text/string field, or in a date field?
Text-speaking, the chart is sorting the items properly by moving from one character to the next, left to right, and putting them in numerical order.
11/12/2019
11/20/2019
11/21/2019
11/24/2019
11/9/2019
12/1/2019
12/2/2019
12/3/2019
12/4/2019
The chart may not recognize this field as a "Date" format, so therefore it will treat it the same way it would treat any other text/string.
Can you create a field with type date, and does it act the same way?
Thanks!
Rachel G
Esri Support Services
Rachel Guttmacher
ArcGIS Online Technology Lead
Esri Support Services