I have tested now and it is working in my test website.
Please clear all caches (server, browser etc) and check if that helps.
Also see browser console if there any js error.

Let me know.

Can you give me access to your website to debug?
If yes, send through https://www.shamimsplugins.com/sensitive-information/ (send wp admin and normal user details, ignore others).

You have send one user account, please create another test user account and send to me so that i can send message between them and debug notification.

I see your website have js error (see screenshot) and it is coming from your theme custom.js file.
Please contact with your theme if your theme added that file. Correcting that error should solve your notification issue.