This field contains duplicate values. Remove all duplicate values and try the operation again.

Question

Greetings Everyone,
I am getting the follow up errors: "This field contains duplicate values. Remove all duplicate values and try the operation again."
when I tried to make the field "Claim Number" from the list in site collection library. See the screen below:
1- I selected on the "List" and I clicked on the list name
"Claim Tracking Report"
2- After I clicked on the list name then I went to the ribbon and selected list setting to choose Enforce Unique for the Field Column
"Claim Number"
3- Then I went down and selected
"Yes" to Enforced the Unique for the Field Column "Claim Number".
4- Then after I clicked "Yes" I got the error
"Sorry, something went wrong. This field contains duplicate values. Remove all duplicate values and try the operation again."  But I don't have any duplicates values Items, because I had them removed before I tried
to Enforce the field column values to Unique. Can someone help or provide me a suggestions on how I can solve this issue please. Thank you
FYI: I am using a Nintex Workflow

Answer 1

Hope this is a list, how many total items are there?
Please try to open this list as access(link in IE) and run this query in access
SELECT Claim.[Claim Number], Count(*) AS Expr1
FROM Claim
GROUP BY Claim.[Claim Number]
HAVING (((Count(*))>1));
Hope it will show something! if this does not show you dups then better to create a separate list and migrate items after configuring unique column.
Please 'propose as answer' if it helped you, also 'vote helpful' if you like this reply.