Sensitivity label mismatch email to user - but not to site administrator

We've set up sensitivity labels for both content and containers like groups and sites. When someone uploads a document with a higher priority sensitivity label to a site that has a lower sensitivity label, it's considered a sensitivity mismatch. This mismatch is recorded in the Purview audit log, and by default, an email alert is sent to both the uploader and the site administrator, as outlined in  https://learn.microsoft.com/en-us/purview/sensitivity-labels-teams-groups-sites#auditing-sensitivity-label-activities) 

However, while we are observing "Detected document sensitivity mismatch" events in the audit log and notifications are being sent to the user, notifications to the site administrator or site owner are not being received. Could anyone shed some light on what might be the issue? Thanks!