We tested the user alert feature and noticed that when a DLP profile is applied to the user activity 'Post' for all web access, the user alert option cannot be selected.

However, once we changed the policy to apply only to specific categories, such as cloud storage, the user alert option became available.

We also observed that user alerts work if no DLP profile is applied but the 'Post' user activity is regulated across all web access.

App Category - Profile - Activity - Action

(1) Specific Category - DLP - Post - User Alert

(2) All Web - DLP - Post - Alert/Block

(3) All Web - No Profile - Post - User Alert

Does anyone know the mechanism behind this behavior?