What are called Notification showing in waitlist

Summary:

I got an incident telling that they are not getting notification which is showing on Waitlist.

I want to know what is called Notification showing in waitlist means?

PFA screenshots of our incident and please let me know what is the issue actually?

How to replicate the issue again.

Thanks & Regards,

Sri Vidya Allada

Content (required):

Version (include the version you are using, if applicable):

Code Snippet (add any code snippets that support your topic, if applicable):