Please check the following two items:
1. On the sorting tab of the object property, please make sure that the Date dimension is listed on the top, so that the data is sorted by Date.
2. There are two Date functions in QlikView/Qlik Sense: Date() and Date#(). The difference between the two functions are detailed in the following post:
Please make sure that you are using the right one. If the input Date value is the text value, you should use Date#() instead.