The following error is reported in the Application Event Viewer:
Application Source:
BEDBG Date: 3/11/2021 13:00:33
Event ID: 259
Task Category: (1)
Level: Error
Keywords:
Classic User: N/A
Computer:
Description: A process crash has been detected. Faulting application: beserver.exe 21.0.1200.1899
Faulting module: beserver.exe 21.0.1200.1899
Fault offset 0x456457
Exception code 0xc0000005.
This issue is resolved in Backup Exec 21.2 R2
Workaround :
Edit Recipient and deselect the checkbox "Send no more than 1 email within 5 minutes"

It is also seen that deselecting the above helped to get the notification to work again in case they stopped after updating to 21.2.