I figured it out on my own by exporting the 'notes' table from another server and copying the correct code to import for the missing table.
You may want to update the code on the aforementioned page so other clients can fix this issue a little bit easier.
When trying to open Notifications in Plesk, I receive the error:
Error: Notification '0' does not exists
I found the following knowledgebase article:
https://support.plesk.com/hc/en-us/articles/214027709-Unable-to-access-notifications-page-Notification-0-does-not-exists
But the first part...