The problem is that Column K also has text entries.
Although the Max() function on its' own ignores these entries, the array formula doesn't and tries to multiply the text values, hence the #VALUE! error.
Try this array formula
Confirm with Ctrl+Shift+Enter not just Enter
It might be that you could use SUBTOTAL() and filters, rather than the array formula.
I have added this to K1
Filter Column D for "WL"
Then
Filter Column N Text > Begins with "Drop "
or whatever your needs might demand.
Hope this helps.
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