When attempting to add specific AD user or group to a rule (under the Users or Groups section), the auto find list does not always populate with the expected AD data.
The size of the result set returned from AD is controlled by a value in the system, which is defaulted to 500.
If the returned set is larger than the set limit, the results will not contain all of the expected results.
This setting is set to increase performance in active directory queries, and console activities. This setting can be increased, but a you should have a discussion about a possible slight performance impact, with a support representative.
Please open a case in the User eXchange referencing this solution.