Tasks not shown in QM12

I have created some custom Notification types according to requirements.

For a given type, tasks are not displayed in QM12.

However, they can be accesed and processed from Notification (QM10 or QM02).

I searched the forum and SAP Notes but could not find any reference to this problem. I guess that must be related to Not. Type, but for other similar types is working OK.

Have you ever experienced this problem ?

Thanks