I would truly convert the calculated string date with another Tableau date conversion calculation with # # to make sure it is a consistent date rather than converting the string field itself to a date type.
Can you give an example?
Maybe you do have the right calc. If you put the newly created date field by itself on a worksheet rows or columns shelf - does it chronologically sort? I can only armchair quarterback this without a workbook.
Please follow the below approach ,as I dont have your workbook so I just copied you data and providing you an alternative.Hope this helps.This is completely based on the situation described above.
Suppose we have data something like below where date is not in sorted order.
Create a combine field by selecting Customer and Date drag that newly created field in between the Customer and Date.
Perform the sorting on that field. Your result will look like the below image.
Now uncheck the header of Combine Field.Right click -> Uncheck Show header. Your Final result will look like the below image