Hi,
Give a clarity on the below things to understand your issue a bit more.
Have you observed in SOST, which notifications are going to someone?
These notifications are related to workflows? Some times notifications will trigger from POWL too, is there any POWL related objects are working in the system?
Check is there any batch jobs other than SWN_SELSEN is running to send the notifications?
Regards,
Murali Krishna.