I've been using the creative cloud package for 3 years. Recently, I've discussed that I do not receive an email notification when a doucment is shared with me. When I go into Adobe to see if any new documents are shown there are none. I used to receive email notifications, not sure what happened. The only way I know a document has been shared is the day after when I receive a brief notification on my windows notification manager.
Hope you are doing well and sorry for the trouble. As described, you don't get the email notification for the documents shared with you.
Would you mind sharing the version of the Adobe Acrobat DC you are using? To check the version go to Help > About Acrobat and make sure you have the latest version installed. Go to Help > Check for Updates and reboot the computer once.
Also, log out of the application, reboot the computer once and re- login using the same adobe ID and password and check if that helps.
I've tried all the items listed above and I'm still not getting the email notifications. My co-workers are still received their notifications. So I think as a group we are correctly sharing the documents.