Notification Disappear from bell notification but available on BPM Worklist

Summary:

Notification missing from Application Notification Section but available in BPM worklist area

Content (please ensure you mask any confidential information):

we have noticed a behavior where the notification disappears from application notification area i.e. Bell, Things to finish or even when you click on bell-->Show All-->Notification section. Check all three tabs on notification screen but notification is not found.

Now we navigate to BPM worklist screen and after applying few filter(Show Task by created date set to ALL) and all the notification even 2 month old are appearing in the list.

Is there some sort of expiry set to notification that they stop appearing on application notification screen and we have to specifically navigate to BPM worklist??