When you concatenate the fields you created a new dimension that is a string - you are sorting on that string not on "Order Prompt"
you have 2 options - the first I am guessing you won't like and that is to change the concatenation order to Order date first =
The second is to include orderdate in the viz and then hide the field
here is the concatenated field
add the oderdate to the viz
and it returns this
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