DLP Incident Issue

I implement Policies on DLP (15.5) and i specify this policies for Specific User Groub From Active Directory

and when i Did this i tested the policy and no incidents appeared to me eventhough there were alot of incidents before i use the User Group Rule To apply this policies to this Groups only,

what shuould i do and could any one faces this issue to tell me the reason and the solution ?

Thank you.