Interesting, but not definitive.

Would you please run these commands on that database and post the results? That will show what indexes SQL "thinks" are missing, and how existing indexes are being used:

USE [DH_KWPN]

SET DEADLOCK_PRIORITY LOW --probably irrelevant, but just in case

DECLARE @list_missing_indexes bit

DECLARE @table_name_pattern sysname

--NOTE: showing missing indexes can take some time; set to 0 if you don't want to wait.

SET @list_missing_indexes = 1 --1=list missing index(es); 0=don't.

PRINT 'Started @ ' + CONVERT(varchar(30), GETDATE(), 120)

IF @list_missing_indexes = 1

BEGIN

SELECT

GETDATE() AS capture_date,

DB_NAME(mid.database_id) AS Db_Name,

OBJECT_NAME(mid.object_id /*, mid.database_id*/) AS Table_Name,

mid.equality_columns, mid.inequality_columns, mid.included_columns,

ca1.max_days_active,

migs.*,

mid.statement, mid.object_id, mid.index_handle

FROM sys.dm_db_missing_index_details mid WITH (NOLOCK)

CROSS APPLY (

SELECT DATEDIFF(DAY, create_date, GETDATE()) AS max_days_active FROM sys.databases WHERE name = 'tempdb'

) AS ca1

LEFT OUTER JOIN sys.dm_db_missing_index_groups mig WITH (NOLOCK) ON

mig.index_handle = mid.index_handle

LEFT OUTER JOIN sys.dm_db_missing_index_group_stats migs WITH (NOLOCK) ON

migs.group_handle = mig.index_group_handle

--order by

--DB_NAME, Table_Name, equality_columns

WHERE

1 = 1

AND mid.database_id = DB_ID()

AND OBJECT_NAME(mid.object_id) IN (

'SHA_PAARDACT',

'SHA_PAARDREGISTER',

'SHA_REGISTER',

'SHA_BOEK'

)

ORDER BY

--avg_total_user_cost * (user_seeks + user_scans) DESC,

Db_Name, Table_Name, equality_columns, inequality_columns

END --IF

PRINT 'Midpoint @ ' + CONVERT(varchar(30), GETDATE(), 120)

-- list index usage stats (seeks, scans, etc.)

SELECT

ius2.row_num, DB_NAME() AS db_name,

i.name AS index_name,

OBJECT_NAME(i.object_id/*, DB_ID()*/) AS table_name,

i.index_id, --ius.user_seeks + ius.user_scans AS total_reads,

dps.row_count,

SUBSTRING(key_cols, 3, 8000) AS key_cols, SUBSTRING(nonkey_cols, 3, 8000) AS nonkey_cols,

ius.user_seeks, ius.user_scans, ius.user_lookups, ius.user_updates,

ius.last_user_seek, ius.last_user_scan, ius.last_user_lookup, ius.last_user_update,

fk.Reference_Count AS fk_ref_count,

FILEGROUP_NAME(i.data_space_id) AS filegroup_name,

ca1.max_days_active,

ius.system_seeks, ius.system_scans, ius.system_lookups, ius.system_updates,

ius.last_system_seek, ius.last_system_scan, ius.last_system_lookup, ius.last_system_update

FROM sys.indexes i WITH (NOLOCK)

INNER JOIN sys.objects o WITH (NOLOCK) ON

o.object_id = i.object_id

CROSS APPLY (

SELECT DATEDIFF(DAY, create_date, GETDATE()) AS max_days_active FROM sys.databases WHERE name = 'tempdb'

) AS ca1

OUTER APPLY (

SELECT

', ' + COL_NAME(object_id, ic.column_id)

FROM sys.index_columns ic

WHERE

ic.key_ordinal > 0 AND

ic.object_id = i.object_id AND

ic.index_id = i.index_id

ORDER BY

ic.key_ordinal

FOR XML PATH('')

) AS key_cols (key_cols)

OUTER APPLY (

SELECT

', ' + COL_NAME(object_id, ic.column_id)

FROM sys.index_columns ic

WHERE

ic.key_ordinal = 0 AND

ic.object_id = i.object_id AND

ic.index_id = i.index_id

ORDER BY

COL_NAME(object_id, ic.column_id)

FOR XML PATH('')

) AS nonkey_cols (nonkey_cols)

LEFT OUTER JOIN sys.dm_db_partition_stats dps WITH (NOLOCK) ON

dps.object_id = i.object_id AND

dps.index_id = i.index_id

LEFT OUTER JOIN sys.dm_db_index_usage_stats ius WITH (NOLOCK) ON

ius.database_id = DB_ID() AND

ius.object_id = i.object_id AND

ius.index_id = i.index_id

LEFT OUTER JOIN (

SELECT

database_id, object_id, MAX(user_scans) AS user_scans,

ROW_NUMBER() OVER (ORDER BY MAX(user_scans) DESC) AS row_num --user_scans|user_seeks+user_scans

FROM sys.dm_db_index_usage_stats WITH (NOLOCK)

WHERE

database_id = DB_ID()

--AND index_id > 0

GROUP BY

database_id, object_id

) AS ius2 ON

ius2.database_id = DB_ID() AND

ius2.object_id = i.object_id

LEFT OUTER JOIN (

SELECT

referenced_object_id, COUNT(*) AS Reference_Count

FROM sys.foreign_keys WITH (NOLOCK)

WHERE

is_disabled = 0

GROUP BY

referenced_object_id

) AS fk ON

fk.referenced_object_id = i.object_id

WHERE

i.object_id > 100 AND

i.is_hypothetical = 0 AND

i.type IN (0, 1, 2) AND

o.type NOT IN ( 'IF', 'IT', 'TF', 'TT' ) AND

(

o.name IN (

'SHA_PAARDACT',

'SHA_PAARDREGISTER',

'SHA_REGISTER',

'SHA_BOEK'

)

)

ORDER BY

--row_count DESC,

--ius.user_scans DESC,

--ius2.row_num, --user_scans+user_seeks

-- list clustered index first, if any, then other index(es)

db_name, table_name, CASE WHEN i.index_id IN (0, 1) THEN 1 ELSE 2 END, index_name

PRINT 'Ended @ ' + CONVERT(varchar(30), GETDATE(), 120)

Edit: Corrected CROSS APPLY column alias.