agree to Graham, check the rules first. - I made the mistake when I did ‘management - tuning’ that I created overrides for too many performance rules. - So take a look on the overrides, too
Besides, check if the SCOM Databases still have sufficient free space and reboot the management servers one by one (if you have 2).
If all not works. - Last, you can also check if the Operations Manager DW is too busy and is not able to do aggregations. - Use the following script ( without warranty ) to check outstanding data aggregations.
WITH AggregationInfo AS (
AggregationType = CASE
WHEN AggregationTypeId = 0 THEN 'Raw'
WHEN AggregationTypeId = 20 THEN 'Hourly'
WHEN AggregationTypeId = 30 THEN 'Daily'
,MIN(AggregationDateTime) as 'TimeUTC_NextToAggregate'
,COUNT(AggregationDateTime) as 'Count_OutstandingAggregations'
,DatasetId FROM StandardDatasetAggregationHistory
WHERE LastAggregationDurationSeconds IS NULL
GROUP BY DatasetId, AggregationTypeId
FROM StandardDataSet AS SDS WITH(NOLOCK)
JOIN AggregationInfo AS AI WITH(NOLOCK) ON SDS.DatasetId = AI.DatasetId
JOIN dbo.StandardDatasetAggregation AS SDA WITH(NOLOCK) ON SDA.DatasetId = SDS.DatasetId AND SDA.AggregationTypeID = AI.AggregationTypeID
ORDER BY SchemaName DESC
Let me know the results