Query plan showing a missing index even though the index is present in the table

In one of my production SQL server instances, a query is taking a long time to run. While checking the query plan, I found that it was giving a suggestion for creating a missing index. I went to the recommended table and found that the suggested index was already present in the table but was somehow not getting used.

Maintenance plans (for rebuilding indexes, updating statistics etc) are done on a regular basis. I am not sure why the index is not getting used? and why query plan keeps on giving suggestion for missing index when it already exists?

The index suggested is exactly the same which is present in the table.

Index usage stats:

OBJECT NAME
INDEX NAME
USER_SEEKS
USER_SCANS
USER_LOOKUPS
USER_UPDATES

Lea_ex1_hs
IX_Lea_ex1_ID
357533
0
0
380386

SQL Server 2008 R2 SP3

Based on the information in your question, I think you've hit a bug that is referenced in Missing index DMVs bug that could cost your sanity… by Paul Randal, and addressed in this Connect item

Per the blog post:

The bug is this: the missing index code may recommend a nonclustered index that already exists. Over and over again. It might also recommend an index that won't actually help a query.

StackExchange Database Administrators Q#149524, answer score: 8