When an entry is updated, the active persistent searches are checked to see if the update causes the entry to satisfy the search criterion specified by the persistent search (scope, filter).
The check above is performed using a (subsidiary) search request and the warning you are seeing indicates that this search failed (returned error) for the entry being modified. As a result, the persistent search may not be updated with the new data.
The next step would be to determine why these searches are failing for you. Some options:
* If the diag-log or query-log is enabled, check for an error around the time of the above warning.
* Raise a support case where we can work with you to determine the cause of the search failure.